J. Physiol. (1976), 259, pp. 771-783 With 5 text-figurem Printed in Great Britain
771
THE EFFECT OF LITHIUM ON THE TRANSPORT OF SODIUM, POTASSIUM AND CHLORIDE BY THE COLON OF NORMAL AND SODIUM-DEPLETED RATS
By DIANA E. M. DOLMAN AND C. J. EDMONDS From the Radioisotopes Division, Clinical Research Centre, Watford Road, Harrow, Middlesex, HAl 3UJ
(Received 7 January 1976) SUMMARY
1. The effect of Li, given systemically or placed in the gut lumen, on the transport of Na, K and C1 and on the transepithelial electrical potential difference (p.d.) was studied in vivo in the distal colon of normal and Na-depleted rats. 2. The specific effect of Li appeared to be on the Na transport system with K and C1 transport affected only indirectly. Active Na absorption was impaired and p.d. reduced when either Li was in the lumen or given systemically. In addition with Li in the lumen, a considerable rise in the plasma-to-lumen Na flux was observed, the flux increasing progressively with rising intraluminal Li concentration. The effects were greater in Na-depleted rats. 3. The greater part of Li absorption from the colon of the rat takes place by exchange for Na, the secretion of which is much enhanced while the p.d. is reduced. This contrasts with human colon in which potassium is the ion exchanged for Li with the p.d. increased. INTRODUCTION
In the preceding paper we reported findings which showed that Li both within the gut lumen and when given systemically, affected the electrical properties of rat colonic epithelium (Dolman & Edmonds, 1976). The observations suggested that the transport of other ions across the epithelium was probably altered by Li, and in the present report we describe the results of experiments undertaken to investigate this aspect in more detail.
772 772
E. M. DOLMAN AND C. J. EDMONDS ~D. METHODS
Male Wistar rats weighing about 300 g were used. They were prepared and maintained as described previously (Dolman & Edmonds, 1976) and the colonic p.d. was measured in a similar manner. All the present experiments were on the distal colon. Systemic Li was administered as a single i.r. injection of Li2SO4 100 mmx. Blood was collected 24 hr later, at the end of the experiment, and the plasma stored at - 10' C until analysed. In the first group of experiments, in which there was partial substitution of choline or Li for Na, the solutions were introduced into a cannulated segment of gut for measurements of ionic flux rate (Edmonds & Marriott, 1970). In all the remaining experiments, the dialysis method, previously described (Dolman & Edmonds, 1975), was used. All solutions were prepared freshly from stock solutions immediately before the experiments. In the first group of experiments, the anion composition included HCO 30 mm in addition to Cl. These solutions had pH 8-2-8-3 which changed little during exposure in the colonic lumen. The results of these and other experiments showed that the addition of HCO3 had no significant effect and in subsequent experiments, HCO3 was not used. 22Na (20 nc/ml.), 42K (200 nc/mi.) or 36CI (1 5 nc/ml.) were added to the luminal solution. In some experiments plasma 22Na clearance was measured 18 hr after i.r. injection of 2 /tC 2 2Na, a tube of dialysis membrane containing either choline chloride 150 rmi or LiCl 150 mm being placed in the colon for 15 min. It was then removed and the 22Na content measured, and blood was collected at the end of the experiment for measurement of the plasma 2 2Na
activity. 22Na and4 2K were counted using a well-type NaI(Th) crystal scintillation counter, and 36CI was counted in a liquid scintillation counter. Na and K concentrations were determined by emission and Li by absorption flame photometry. Cl was measured with an EEL chloride meter. Remults are given was mean values+± .E. of mean. Fluxes are expressed per centimetre of gut length, the latter being determined by the length of the dialysis tube. Jm. represents the unidirectional flux from lumen to plasma, Jm from plasma to lumen. J.et is the net flux, a positive sign indicating net absorption, a negative sign net secretion.
RESULTS
Effects of Li in the gut lumen on ionic fluxes Comparison of choline and Li. The effect of partial substitution of choline or Li for Na was examined in the distal colon of groups of normal and Na-depleted rats (Fig. 1). In these experiments, the gut lumen was first rinsed with the test solution, which remained in the lumen for 20 min before the flux measurements were made. The three solutions used contained NaHCO3 30 mm and in addition NaCl, choline chloride or LiCl 120 mm. Measurements were made with each solution in turn in the order shown in Fig. 1 and then again with the initial solution. The results showed that when the Na concentration was reduced by substitution of choline there was a considerable fall of lumen-to-plasma
773 LITHIUM ON IONIC ABSORPTION flux, Jm. When, however, the flux rates were determined with LiCl in the lumen, the value of Jms was little changed compared with choline chloride in the normal rats, but in the Na-depleted it was significantly less (P < 0.025) than in the choline experiments. The flux Jm increased in both groups when Li was substituted for choline. The result was that in both groups of animals there was considerable secretion of Na when Li was present in the lumen. Na-depleted
Normal
Mean p.d. (mV)
11.8
8-4
50
9-5
31-1
10-7
6-3
16-0
500 s E400 Z E
IT
JmsNa
JmsNa
Jsm Na
300
ismNa
ii10E 200
x
K
100
K Na Na 30 Na 30 150 Choi 120 Li 120
Na Na Na 30 Na 30 150 1 50 Choi 120 Li 120 Luminal solutions
Na 150
Fig. 1. Effect on Na fluxes and K secretion of substituting choline or Li for Na in the luminal solution in the distal colon of seven normal and nine Na-depleted rats. The anion composition was maintained constant throughout, Cl 120 mM, HCO3 30 mM.
In the normal rats the K secretion rate was essentially unaltered with the changes of the luminal solution, while in the Na-depleted rats the K secretion rate was reduced (P < 0.05) by both Li and choline, to a similar degree. Thus in contrast with the effects on p.d. and Na fluxes, choline and Li were similar in regard to effects on K secretion. The final set of measurements, done 30-50 min after the Li had been completely removed from the lumen, showed that a considerable degree of recovery had occurred, but neither the p.d. nor the Na fluxes had returned completely to their pre-Li values. The findings were consistent with the p.d. observations (Dolman & Edmonds, 1976) which showed that about 2 hr were necessary for restoration of the p.d. after some minutes of exposure to Li containing solutions.
D. E. M. DOLMAN AND C. J. EDMONDS Na and K secretion into Na-free solutions. Secretion rates of Na and K were also measured while solutions of choline chloride 150 mm or LiCi 150 mm were in the lumen. Measurements of plasma 22Na clearance were made over a 15 min period in order to minimize the rise of luminal Na 774 774
concentration resulting from Na diffusion into the lumen. The secretion considerably greater into the LiCl solution than into the choline chloride in both normal and Na-depleted rats (Table 1). The
rate of Na was
TABLE 1. Plasma-to-lumen flux of Na and secretion rate of K when the lumen in the distal colon contained either choline Cl 150 num or LiCi 150 rnm Plasma-to-lumen Na flux
K secretion rate
(J~m) (n-mole min-' cm-') (n-mole min-' cm-') Choline chloride 6(24)223± 13
n
Normal
LiCl
583+±23
Choline chloride -14+ 2 - 99 ±8
LiCl -17+ 3 - 50± 6
734 ±28 Na-depleted 6(24)128+±10 In this and subsequent tables the number in parentheses refers to the number of flux measurements carried out.
results showed that when choline chloride was present, Na secretion rate in the depleted rats was lower than in the normal rats, but when LiCl was present the reverse was true, Na secretion rate being greater in the Na-depleted rats. In the case of K the secretion rate was unaffected by substituting LiCl for for choline chloride in the normal rats, but in the Na-depleted rats the change caused a marked fall in secretion rate.
Effect of various concentrations of Li in the luminal solution In this series of experiments flux measurements were made when the luminal NaCl concentration was maintained at 50 mmv with various concentrations of Li2SO4 present in addition. Mannitol was added to the solutions as necessary so that all were isotonic. When Li was absent from the lumen there was, in the normal rats, some secretion of Na but in the Na-depleted rats considerable absorption occurred (Fig. 2). The addition of Li had little effect on Jm. in the normal rats but in the Na-depleted rats Jms, fell progressively as the luminal Li concentration was increased. With the opposite flux, Jsm, there was in all the rats a progressive rise as the Li concentration was increased although again the changes were more evident in the Na-depleted animals. Thus J~sm rose by about 3.5% in the normal rats as the Li concentration was
LITHIUM ON IONIC ABSORPTION 775 increased to 100 mm as against a rise of 100-200 % in the Na-depleted rats. The effect of Li on Cl fluxes was also examined in groups of normal and Na-depleted rats (Table 2). In these experiments the lumen contained a solution having NaCl concentration 50 mm and LiCl concentration 100 mM. In the normal rats the presence of Li did not appear to affect the Cl fluxes significantly. In the Na-depleted rats, however, both unidirectional fluxes were increased, although the net flux did not alter significantly. Jism 500 ,,I
Jsm .C E
400
I
1
E U
300 Eu
z 200 1
a .&
0
Jms a
ims
x
100 1 M
.
0
50
N
2
100 0 Concentration of Li in lumen (mm)
A
s
50
100
Fig. 2. Na unidirectional fluxes in the distal colon of six normal and six Na-depleted rats when various concentrations of Li were in the lumen. Concentration of Na was constant at 50 mm. TABLE 2. The effect of Li in the lumen of the distal colon
Luminal solution NaCl 50 mm Choline Cl 100 mM NaCl 50 mM LiCl 100 mM P
on
the Cl fluxes
Normal
Na depleted
&s Js (n-mole min1' cm-') 6(15) 183±7 538+15 355+13
I. Jon (n-mole min- cm-L) 6(16) 174±8 424+12 250+13
n
J.-f
n
Junket
6(21) 181±11 569±20 388±14 6(22) 176±8 561+12 385+13 n.s.
n.s.
n.s.
n.s.
771
THE EFFECT OF LITHIUM ON THE TRANSPORT OF SODIUM, POTASSIUM AND CHLORIDE BY THE COLON OF NORMAL AND SODIUM-DEPLETED RATS
By DIANA E. M. DOLMAN AND C. J. EDMONDS From the Radioisotopes Division, Clinical Research Centre, Watford Road, Harrow, Middlesex, HAl 3UJ
(Received 7 January 1976) SUMMARY
1. The effect of Li, given systemically or placed in the gut lumen, on the transport of Na, K and C1 and on the transepithelial electrical potential difference (p.d.) was studied in vivo in the distal colon of normal and Na-depleted rats. 2. The specific effect of Li appeared to be on the Na transport system with K and C1 transport affected only indirectly. Active Na absorption was impaired and p.d. reduced when either Li was in the lumen or given systemically. In addition with Li in the lumen, a considerable rise in the plasma-to-lumen Na flux was observed, the flux increasing progressively with rising intraluminal Li concentration. The effects were greater in Na-depleted rats. 3. The greater part of Li absorption from the colon of the rat takes place by exchange for Na, the secretion of which is much enhanced while the p.d. is reduced. This contrasts with human colon in which potassium is the ion exchanged for Li with the p.d. increased. INTRODUCTION
In the preceding paper we reported findings which showed that Li both within the gut lumen and when given systemically, affected the electrical properties of rat colonic epithelium (Dolman & Edmonds, 1976). The observations suggested that the transport of other ions across the epithelium was probably altered by Li, and in the present report we describe the results of experiments undertaken to investigate this aspect in more detail.
772 772
E. M. DOLMAN AND C. J. EDMONDS ~D. METHODS
Male Wistar rats weighing about 300 g were used. They were prepared and maintained as described previously (Dolman & Edmonds, 1976) and the colonic p.d. was measured in a similar manner. All the present experiments were on the distal colon. Systemic Li was administered as a single i.r. injection of Li2SO4 100 mmx. Blood was collected 24 hr later, at the end of the experiment, and the plasma stored at - 10' C until analysed. In the first group of experiments, in which there was partial substitution of choline or Li for Na, the solutions were introduced into a cannulated segment of gut for measurements of ionic flux rate (Edmonds & Marriott, 1970). In all the remaining experiments, the dialysis method, previously described (Dolman & Edmonds, 1975), was used. All solutions were prepared freshly from stock solutions immediately before the experiments. In the first group of experiments, the anion composition included HCO 30 mm in addition to Cl. These solutions had pH 8-2-8-3 which changed little during exposure in the colonic lumen. The results of these and other experiments showed that the addition of HCO3 had no significant effect and in subsequent experiments, HCO3 was not used. 22Na (20 nc/ml.), 42K (200 nc/mi.) or 36CI (1 5 nc/ml.) were added to the luminal solution. In some experiments plasma 22Na clearance was measured 18 hr after i.r. injection of 2 /tC 2 2Na, a tube of dialysis membrane containing either choline chloride 150 rmi or LiCl 150 mm being placed in the colon for 15 min. It was then removed and the 22Na content measured, and blood was collected at the end of the experiment for measurement of the plasma 2 2Na
activity. 22Na and4 2K were counted using a well-type NaI(Th) crystal scintillation counter, and 36CI was counted in a liquid scintillation counter. Na and K concentrations were determined by emission and Li by absorption flame photometry. Cl was measured with an EEL chloride meter. Remults are given was mean values+± .E. of mean. Fluxes are expressed per centimetre of gut length, the latter being determined by the length of the dialysis tube. Jm. represents the unidirectional flux from lumen to plasma, Jm from plasma to lumen. J.et is the net flux, a positive sign indicating net absorption, a negative sign net secretion.
RESULTS
Effects of Li in the gut lumen on ionic fluxes Comparison of choline and Li. The effect of partial substitution of choline or Li for Na was examined in the distal colon of groups of normal and Na-depleted rats (Fig. 1). In these experiments, the gut lumen was first rinsed with the test solution, which remained in the lumen for 20 min before the flux measurements were made. The three solutions used contained NaHCO3 30 mm and in addition NaCl, choline chloride or LiCl 120 mm. Measurements were made with each solution in turn in the order shown in Fig. 1 and then again with the initial solution. The results showed that when the Na concentration was reduced by substitution of choline there was a considerable fall of lumen-to-plasma
773 LITHIUM ON IONIC ABSORPTION flux, Jm. When, however, the flux rates were determined with LiCl in the lumen, the value of Jms was little changed compared with choline chloride in the normal rats, but in the Na-depleted it was significantly less (P < 0.025) than in the choline experiments. The flux Jm increased in both groups when Li was substituted for choline. The result was that in both groups of animals there was considerable secretion of Na when Li was present in the lumen. Na-depleted
Normal
Mean p.d. (mV)
11.8
8-4
50
9-5
31-1
10-7
6-3
16-0
500 s E400 Z E
IT
JmsNa
JmsNa
Jsm Na
300
ismNa
ii10E 200
x
K
100
K Na Na 30 Na 30 150 Choi 120 Li 120
Na Na Na 30 Na 30 150 1 50 Choi 120 Li 120 Luminal solutions
Na 150
Fig. 1. Effect on Na fluxes and K secretion of substituting choline or Li for Na in the luminal solution in the distal colon of seven normal and nine Na-depleted rats. The anion composition was maintained constant throughout, Cl 120 mM, HCO3 30 mM.
In the normal rats the K secretion rate was essentially unaltered with the changes of the luminal solution, while in the Na-depleted rats the K secretion rate was reduced (P < 0.05) by both Li and choline, to a similar degree. Thus in contrast with the effects on p.d. and Na fluxes, choline and Li were similar in regard to effects on K secretion. The final set of measurements, done 30-50 min after the Li had been completely removed from the lumen, showed that a considerable degree of recovery had occurred, but neither the p.d. nor the Na fluxes had returned completely to their pre-Li values. The findings were consistent with the p.d. observations (Dolman & Edmonds, 1976) which showed that about 2 hr were necessary for restoration of the p.d. after some minutes of exposure to Li containing solutions.
D. E. M. DOLMAN AND C. J. EDMONDS Na and K secretion into Na-free solutions. Secretion rates of Na and K were also measured while solutions of choline chloride 150 mm or LiCi 150 mm were in the lumen. Measurements of plasma 22Na clearance were made over a 15 min period in order to minimize the rise of luminal Na 774 774
concentration resulting from Na diffusion into the lumen. The secretion considerably greater into the LiCl solution than into the choline chloride in both normal and Na-depleted rats (Table 1). The
rate of Na was
TABLE 1. Plasma-to-lumen flux of Na and secretion rate of K when the lumen in the distal colon contained either choline Cl 150 num or LiCi 150 rnm Plasma-to-lumen Na flux
K secretion rate
(J~m) (n-mole min-' cm-') (n-mole min-' cm-') Choline chloride 6(24)223± 13
n
Normal
LiCl
583+±23
Choline chloride -14+ 2 - 99 ±8
LiCl -17+ 3 - 50± 6
734 ±28 Na-depleted 6(24)128+±10 In this and subsequent tables the number in parentheses refers to the number of flux measurements carried out.
results showed that when choline chloride was present, Na secretion rate in the depleted rats was lower than in the normal rats, but when LiCl was present the reverse was true, Na secretion rate being greater in the Na-depleted rats. In the case of K the secretion rate was unaffected by substituting LiCl for for choline chloride in the normal rats, but in the Na-depleted rats the change caused a marked fall in secretion rate.
Effect of various concentrations of Li in the luminal solution In this series of experiments flux measurements were made when the luminal NaCl concentration was maintained at 50 mmv with various concentrations of Li2SO4 present in addition. Mannitol was added to the solutions as necessary so that all were isotonic. When Li was absent from the lumen there was, in the normal rats, some secretion of Na but in the Na-depleted rats considerable absorption occurred (Fig. 2). The addition of Li had little effect on Jm. in the normal rats but in the Na-depleted rats Jms, fell progressively as the luminal Li concentration was increased. With the opposite flux, Jsm, there was in all the rats a progressive rise as the Li concentration was increased although again the changes were more evident in the Na-depleted animals. Thus J~sm rose by about 3.5% in the normal rats as the Li concentration was
LITHIUM ON IONIC ABSORPTION 775 increased to 100 mm as against a rise of 100-200 % in the Na-depleted rats. The effect of Li on Cl fluxes was also examined in groups of normal and Na-depleted rats (Table 2). In these experiments the lumen contained a solution having NaCl concentration 50 mm and LiCl concentration 100 mM. In the normal rats the presence of Li did not appear to affect the Cl fluxes significantly. In the Na-depleted rats, however, both unidirectional fluxes were increased, although the net flux did not alter significantly. Jism 500 ,,I
Jsm .C E
400
I
1
E U
300 Eu
z 200 1
a .&
0
Jms a
ims
x
100 1 M
.
0
50
N
2
100 0 Concentration of Li in lumen (mm)
A
s
50
100
Fig. 2. Na unidirectional fluxes in the distal colon of six normal and six Na-depleted rats when various concentrations of Li were in the lumen. Concentration of Na was constant at 50 mm. TABLE 2. The effect of Li in the lumen of the distal colon
Luminal solution NaCl 50 mm Choline Cl 100 mM NaCl 50 mM LiCl 100 mM P
on
the Cl fluxes
Normal
Na depleted
&s Js (n-mole min1' cm-') 6(15) 183±7 538+15 355+13
I. Jon (n-mole min- cm-L) 6(16) 174±8 424+12 250+13
n
J.-f
n
Junket
6(21) 181±11 569±20 388±14 6(22) 176±8 561+12 385+13 n.s.
n.s.
n.s.
n.s.
