The proton-activated inward current of rat sensory neurons includes a calcium component.
Many neurons possess a proton-activated conductance, IH, which supports a large transient inward current at negative potentials and thereby depolarizes cells during rapid drops in external pH. The channels underlying this conductance are permeant to monovalent cations, with a clear preference for sodium. In earlier experiments, it appeared that divalent cations were impermeant: increasing concentrations of extracellular Ca2+ actually decreased the current amplitude. Using whole-cell patch clamp recording techniques, we find that the proton-activated channel is permeant to Ca2+ ions. In the absence of monovalent cations, a substantial current is supported by divalent cations. The previously reported block results from competition between divalents and monovalents. This finding suggests that IH may provide a pathway for Ca2+ entry during the acidification that accompanies normal synaptic transmission, excessive electrical activity, and tissue ischemia.
Kovalchuk YuN
A.A. Bogomoletz Institute of Physiology, Ukrainian Academy of Sciences, Kiev, U.S.S.R.
Krishtal
O A
OA
Nowycky
M C
MC
D000818:Animals; D002118:Calcium / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009475:Neurons, Afferent / Q000502:physiology*; D051381:Rats; D012964:Sodium / Q000502:physiology; D012668:Trigeminal Ganglion / Q000502:physiology*
D012964:Sodium; D002118:Calcium