Functional Interaction of the Calcium Channel Subunits

HORMONAL REGULATION OF THE SMOOTH MUSCLE CALCIUM CHANNEL 

The opening and closing of L-type calcium channels is controlled by the membrane potential. In addition, the p-adrenergic receptor controls the availability of the channel to open upon membrane depolarization. Isoproterenol increases the cardiac calcium current three- to sevenfold either by cAMP-dependent phosphorylation of the channel (Kameyama et al., 1985 Hartzell and Fischmeister, 1992) or by the activated a subunits of the trimeric GTP binding protein Gs (Yatani and Brown, 1989) or by a combination of the activated a subunits of the trimeric GTP binding protein Gg and the active cAMP kinase (Cavalie et al., 

The L-type calcium current of isolated tracheal smooth muscle cells is also stimulated by the activation of the p-adrenergic receptor (Welling et al., 1992). This p-adrenergic receptor effect is mediated directly by a G-protein and not by cAMP kinase activation. Isoproterenol also increased the L-type calcium current in isolated smooth muscle cells from rabbit ear 

We thank Mrs. I. Schatz for typing the manuscript. The results obtained in the authors laboratory were supported by grants from Deutsche Forschungsgemeinschaft and Fond der Chemie. 

Hullin, R., Freundner, S., Singer, D., Dascal, N., Flockerzi, 

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