Licking for taste solutions by potassium-deprived rats: specificity and mechanisms

Abstract

There has been little work on the specificity and mechanisms underlying the appetite of potassium (K(+)) deprived rats, and there are conflicting results. To investigate the contribution of oral factors to changes in intake induced by K(+) deficiency, we conducted two experiments using 20-s "brief access" tests. In Experiment 1, K(+)-deprived rats licked less for water than did replete rats. After adjusting for this difference, K(+)-deprived rats exhibited increased licking for 100 mM CaCl(2), 100 mM MgCl(2), and 100 mM FeCl(2) compared with K(+)-replete rats. In Experiment 2, which used larger rats, the K(+)-deprived and replete groups licked equally for water, 500 mM Na.Gluconate, 350 mM KCl, 500 mM KHCO(3), and 1 mM quinine.HCl, but the K(+)-deprived rats licked more for 500 mM KCl, 500 mM CsCl, and 500 mM NaCl than did the replete rats. Licking was unaffected by addition to NaCl of 200 muM amiloride, an epithelial Na(+) channel (ENaC) blocker, or 100 muM ruthenium red, a vanilloid receptor 1 (VR-1) antagonist, or by addition to KCl of 50 muM 4-aminopyridine, a K(+) channel blocker. These findings suggest that K(+)-deprivation produces a non-specific appetite that is guided by oral factors. We found no evidence that this response was mediated by ENaC, VR-1, or K(+) channels in taste receptor cells.

Fig. 1

A. Mean (+SEM) plasma K⁺ concentrations of K⁺-deprived and replete rats on the fourth day of water training (Pre-Test) and following the last brief access testing session in Experiment 1 (Post-Test). K⁺-deprived rats had significantly lower plasma K⁺-concentrations as indicated by a statistically significant main effect of deprivation group, with no group × test-phase interaction. B. Mean (+SEM) 24-h intakes of 200 mM KCl and dH₂O by K⁺-deprived and replete rats following brief access testing. The lack of an effect of group indicates total fluid consumption did not differ between groups, but the statistically significant taste solution × group interaction indicates that K⁺-deprived and replete rats differed in their solution preferences. B, inset. Mean (+SEM) ratios of 24-h 200 mM KCl intake: 24-h dH₂O intake in the two-bottle preference tests. K⁺-deprived rats exhibited a robust preference for KCl that was not observed in replete rats. (*, significantly different from replete rats, p < 0.05)

Fig. 2

Mean (+SEM) licks (in 20-s trials) for an array of taste solutions by K⁺-deprived and replete rats in Experiment 1. Relative to replete rats, K⁺-deprived rats licked more 100 mM CaCl₂ and 100 mM MgCl₂ but less dH₂O, 10 mM citric acid, 100 mM sucrose, and 200 mM KHCO₃. Group differences in taste evaluation of NaCl and KCl solutions may have been masked by the fact that both K⁺-deprived and replete rats licked maximally for these solutions. Inset. Analysis of taste solutions for which lick responses were well below the maximal lick rate. Mean (+SEM) ratios of brief access licking for 100 mM CaCl₂, 100 mM MgCl₂, 100 mM FeCl₂ and 10 mM citric acid relative to the number of licks expressed for water. Relative to replete rats, K⁺-deprived rats showed significant increases in licking for the chloride-containing salt solutions. (*, significantly different from replete rats, p < 0.05)

Fig. 3

A. Mean (+SEM) licks (in 20-s trials) for dH₂O by K⁺-deprived and replete rats during days 3–7 of training of Experiment 1. A significant effect of group suggests that K⁺-deprived rats licked less than replete rats during water training trials. B. Mean (+SEM) ratios of licking to body weight for dH₂O training trials. No group differences were apparent, suggesting that the reduction in thirst in the K⁺-deprived rats relative to the replete rats may have been due to group differences in weight rather than to a more specific effect of K⁺-deprivation.

Fig. 4

A. Mean (+SEM) K⁺ concentrations in urine samples collected overnight before the first (Pre-Test) and after the last (Post-Test) brief access testing session from K⁺-deprived and replete rats in Experiment 2. K⁺-deprived rats had significantly lower urine K⁺ concentrations than replete rats both before and after testing, confirming that the K⁺ deprivation protocol effectively induced K⁺ deficiency. B. Mean (+SEM) 24-h intakes of 200 mM KCl and dH₂O by K-deprived and replete rats following brief access testing. B, inset. Mean (+SEM) ratios of 24-hr 200 mM KCl intake: 24-h dH₂O intake in the two-bottle preference tests. K⁺-deprived rats preferred 200 mM KCl to dH₂O (ratio < 1), whereas replete rats exhibited the opposite preference (ratio > 1). (*, significantly different from replete rats, p < .05)

Fig. 5

A. Mean (+SEM) licks (in 20-s trials) for dH₂O by K⁺-deprived and replete rats during days 3–5 of training of Experiment 2. No group differences were apparent. B. Mean (+SEM) ratios of licking to body weight for dH₂O training trials. Again, K⁺-deprived rats did not differ from replete rats.

Fig. 6

Mean (+SEM) licks (in 20 s trials) for an array of taste solutions by K⁺-deprived and replete rats in Experiment 2. K⁺-deprived rats licked significantly more for 500 mM KCl, 500 mM CsCl, 500 mM KCl+50 μM 4-aminopyridine (4-AP), 500 mM NaCl, and 500 mM NaCl+100 μM Ruthernium Red (RR) than did deprived rats.