ISSN:
1432-2013
Keywords:
Key words L-type Ca channel
;
Magnesium
;
Phosphorylation
;
Frog
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The effect of phosphorylation on the intracellular Mg2+ concentration-dependent change in Ca channel activity was examined using the patch clamp technique. The kinetic changes in Ca channels induced either by phosphorylation [1 μM forskolin (FSK) plus 50 μM isobutylmethylxanthine (IBMX)] or by lowering intracellular [Mg2+] ([Mg2+]i) are qualitatively identical: an increase in both the open probability and availability of channels, as well as a decrease in the closed time without a change in the mean open time. This suggests that the mechanism for the increase in activity of Ca channels shares a common pathway of kinetic change. The concentration/response curve for the Mg2+-evoked modification of calcium channels was altered greatly by channel phosphorylation. In the external medium containing 1 μM FSK + 50 μM IBMX, Ca channels recorded with pipettes containing okadaic acid (OA) lost their sensitivity to Mg2+ in the range 1 × 10–6 M–1 × 10–3 M and remained in a fully active state. On the contrary, under basal conditions, the activity of Ca channel was strongly dependent on the internal Mg2+ over the same range of [Mg2+]. Similarly, phosphorylation of Ca channels eliminated the blocking action of guanosine triphosphate observed under basal conditions. A model is proposed in which Ca channels are equipped with regulatory gates for opening and closing the channels, and their regulation is dependent on [Mg2+]i and the degree of phosphorylation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s004240050519
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