Kinetic properties and selectivity of calcium‐permeable single channels in Aplysia neurones.

Abstract

SUMMARY1. Two kinds of single channels, carrying inward currents even above the Na and Cl ion equilibrium potentials, were observed in outside-out patches from Aplysia neurones bathed in K-free internal and external solutions. The channel carrying the larger elementary current has been studied in detail.2. When the internal solution contained mainly CsCl, this channel usually inactivated during the first minutes following isolation of the membrane patch. However, when the internal solution contained NaCl instead of CsCl, the channel remained functional during several hours, thus allowing the present study.3. Na-Tris, NaCl-mannitol and Ca-Ba external substitution experiments showed that the channel studied is much more permeable to divalent cations than to sodium ions. 12. The possible relationships between this channel and previously described 'Ca channels' and 'slow inward currents' are discussed.

Voltage-independent barium-permeable channel activated inLymnaea neurons by internal perfusion or patch excision

“…A divalent-selective channel in Aplysia that has several characteristics in common with the HP channels described here has been reported (Chesnoy-Marchais, 1985). The activation of this channel, like HP channels, is not strongly dependent upon voltage, being quite active at negative potentials.…”

Suppression of calcium current by an endogenous neuropeptide in neurones of Aplysia californica.

“…13B and C) and, assuming the different classes of Ca2+ channels to be activated at different potentials, the reduced effectiveness of FMRFamide in suppressing Ca2+ current at potentials below + 10 mV. Two or more types of Ca2+ channels have been reported in Aptysia neurones (Chesnoy-Marchais, 1985;Strong et al 1986). …”

Nonselective cation channel activated by patch excision from lobster olfactory receptor neurons

“…A third and smaller group consists of nonselective cation channels activated by patch excision. These channels have previously been de-* Present address: Section of Molecular Neurobiology, Yale University School of Medicine, 333 Cedar St., New Haven, CT 06510. scribed only in molluscan neurons (Chesnoy-Marchais, 1985;Strong et al, 1987;Yazejian & Byerly, 1989). They have a relatively high conductance for divalent cations, are voltage independent or only weakly voltage dependent, and have conductances and kinetic properties dependent upon the types and quantities of permeant cations present.…”