A quantitative study of the dependence of feline cold receptor activity on the calcium concentration.

An isolated preparation of the cat tongue was developed to study quantitatively the relation between single cold receptor activity and calcium concentration. The activity recorded from lingual cold fibres of the isolated preparation was identical to that observed by previous authors in lingual cold receptors of whole animals. A perfusing solution containing excess calcium (5 mmol/l) suppressed discharge at constant temperatures as well as the dynamic response to rapid cooling. Reduced calcium levels (0.5 mmol/l) enhanced cold fibre activity at adapting temperatures above 15 degrees C. Cold receptor activity was linearly inversely related to the logarithm of calcium concentration at adapting temperatures above 20 degrees C. The linear relation was valid for both the discharge at constant temperatures and the dynamic peak frequency during cooling steps. From this relation it was calculated that at 25 degrees C an elevation of 0.1 mmol/l external calcium above the control value (1.53 mmol/l) reduces static firing rate by 0.35 impulses per second. It is concluded that neither the in vitro conditions nor the application of various external calcium concentrations impair cold receptor function. The data are consistent with the hypothesis of a calcium-stimulated outward current controlling the static and dynamic response characteristics of cold receptors.