AJP - Cell Physiology, Vol 235, Issue 5 180-C187, Copyright © 1978 by American Physiological Society
Ionic milieu and control of K permeability in the parotid gland
J. W. Putney Jr
The roles of Mg, K, Na, and Cl ions in the biphasic K-permeability response
(86Rb release) to receptor activation in the parotid gland were
investigated. Both the transient and sustained phases of K release (86Rb
release) were unaffected by alterations in Mg concentration. Elevating
extracellular K enhanced 86Rb release presumably by decreasing the
negativity of the membrane potential. Elevating extracellular K had no
effect on the transient or sustained phases of 86Rb release due to
carbachol and 1.0 mM Ca. Measurements of responses to carbachol with
various substitutes for NaCl suggested that extracellular Cl and ionic
strength are important for the K-permeability response. Experiments with
LiCl suggested the operation of a Na-Ca exchange similar to that seen
earlier in experiments with amylase release. When tetraethylammonium Cl was
substituted for NaCl, the cation appeared to block K fluxes directly.
Choline Cl, in partial substitution for NaCl, potentiated the sustained
phase of response to substance P and, in complete substitution, produced
both Ca-dependent and Ca-independent increases in 86Rb release. It was
concluded that the 86Rb-release response in relatively (but not completely)
insensitive to alteration in the ionic milieu. It was also concluded that
Na regulates K permeability in part directly and in part by means of a
Na-Ca exchange.
