Static and dynamic activity of cold receptors at various calcium levels.

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Abstract
The effect of changed blood Ca levels on the impulse pattern of nasal cold fibers in cats was studied at various constant temperatures and during rapid cooling from various adapting levels. Ca levels were increased by i.v. infusion of calcium gluconate and decreased by the chelating agent EDTA. At constant temperatures the mean discharge rate of all fibers tested was reduced by Ca and elevated by EDTA. During 5.degree. C cooling steps, the dynamic peak frequency was only slightly affected by Ca or EDTA, whereas the cumulative number of impulses was decreased by Ca and increased by EDTA. EDTA elicited a grouped or burst discharge in previously nonbursting fibers. An already existing burst discharge was enhanced by EDTA and suppressed by Ca. The temperature dependence of the EDTA-induced burst discharge corresponded to that of a natural burst discharge. Burst discharges at constant temperatures and transient burst discharges following rapid cooling were affected by EDTA in the same way; both exhibited a similar temperature dependence. Ca removal induces a depolarization of the cold-receptor membrane by a reduced activation of a Ca-dependent outward current, whereas Ca application enhances the activation of this system. A comparison of the burst parameters of cold fibers and of molluscan pacemaker neurons supports the hypothesis that the cold-receptor membrane possesses a potential dependent feedback system similar to that described for molluscan neurons.

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