Injections of calcium ions into spinal motoneurones

Abstract

SUMMARY1. In cats under Dial anaesthesia, Ca2+ was injected inside lumbosacral motoneurones, by passing currents between CaCl2-and KCl-containing barrels of compound micropipettes.2. There was a reduction in excitability and a fall in membrane resistance, both rapid in onset and quickly reversible. 4. The most common change in membrane potential was a hyperpolarization; but in nearly half the cases, there was no clear change or a small depolarization. A reversal level for the effect of Ca2+ could be measured in five cells: on the average, it was 10 mV more negative than the resting potential.5. Observations on i.p.s.p.s showed that Ca2+ probably does not alter gC: it was concluded that the fall in membrane resistance caused by intracellular Ca2+ is mainly due to an increase in gK.6. These results confirm previous suggestions that a steep transmembrane gradient of Ca2+ is essential for the maintenance of a low membrane conductivity, and that a rise in internal free Ca2+ -whether due to influx or release from internal stores -may play an important role in regulating neuronal activity.

A potassium contribution to the response of the barnacle photoreceptor.

“…A Ca2+-induced K+ current is known to exist in various types of neurones (Meech, 1972(Meech, , 1974Krnjevi6 & Lisiewicz, 1972;Krnjevi6, Puil & Werman, 1975;Brown & Brown, 1973) and was suggested for the scallop photoreceptor . In those cases the conductance changes decay within at least several seconds, but it appears that the time course may depend on the experimental procedures.…”

International Union of Basic and Clinical Pharmacology. C. Nomenclature and Properties of Calcium-Activated and Sodium-Activated Potassium Channels

“…Intracellular injection of Ca 2+ into neurons of both invertebrates and vertebrates was subsequently found to activate a K + conductance (Krnjevi c and Lisiewicz, 1972;Meech, 1972). The discovery of a Drosophila mutant termed slowpoke (slo) (Elkins et al, 1986), in which a Ca 2+ -dependent component of K + current is lacking in indirect flight muscles, eventually led to the identification of the first gene that encodes a Ca 2+ -activated K + channel (Atkinson et al, 1991;Adelman et al, 1992) and its mammalian homolog (Butler et al, 1993).…”

Augmentation by calcium channel antagonists of general anaesthetic potency in mice

“…Ethanol has been shown to decrease calcium entry via voltage-dependent channels (Lynch & Littleton, 1983) and also via voltageindependent channels (Stokes & Harris, 1982). On the other hand Baker & Shapira (1980) suggested that anaesthetics increased sensitivity of endogenous calcium binding proteins in the absence ofany alterations in intracellular calcium levels, while Krnjevic & Lisiewicz (1972) suggested that a rise in intracellular calcium activated calcium-sensitive forms of K+ and C1-permeability systems resulting in reduced 'Address for correspondence: Univ. Dept.…”