Biochemical and Biophysical Research Communications 2001-01-12

Inhibition of CaT1 channel activity by a noncompetitive IP3 antagonist.

P M Vassilev, J B Peng, J Johnson, M A Hediger, E M Brown

Index: Biochem. Biophys. Res. Commun. 280(1) , 145-50, (2001)

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Abstract

A newly cloned, human epithelial Ca2+ transport protein (CaT1) was expressed in Xenopus laevis oocytes, and its single channel characteristics were examined. The CaT1 channel shows a strong dependence upon hyperpolarizing voltages, being activated by very negative voltages. The probability of channel opening and mean open times increase substantially at more negative voltages in the range of -90 to -160 mV. In addition, CaT1 channel activity was markedly inhibited by micromolar levels of a noncompetitive antagonist of the IP3 receptor originally isolated from a marine sponge, Xestospongin C. This inhibitory effect could be mediated indirectly via the binding of Xestospongin C to the inositol-trisphosphate (IP3) receptor or, alternatively, by a direct action on the CaT1 channel itself. Independent of its mechanism of action in inhibiting CaT1, Xestospongin C will provide a useful tool for elucidating the physiological role(s) of this novel epithelial Ca2+ channel.Copyright 2001 Academic Press.