Modulation by dihydropyridines and protein kinases of the recombinant cardiac L-type Ca channel with multiple unitary current amplitudes.

The cloned cardiac L-type Ca channel current expressed in baby hamster kidney (BHK) cells was characterized at the single channel level. After transfection of cDNA of the cardiac alpha 1 subunit along with skeletal beta, alpha 2/delta and gamma subunits to this cell line, recombinant Ca channels could be observed at high density over extended times. The properties of cloned Ca channels were almost identical with those of native cardiac L-type Ca channels, with respect to voltage dependence of activation, unitary conductance (25 pS with 100mM Ba2+ as the charge carrier and the modulation by a dihydropyridine (DHP) Ca channel agonist and an antagonist, or by 8Br-cAMP and phorbol esters. As in native cardiac Ca channels, changes in kinetic behavior during 8Br-cAMP application included increased number of channel openings and increased duration of open times. Phorbol esters also increased the number of openings with long duration. In 27 out of 37 patches in the presence of BayK8644, small amplitude openings of several levels were observed. These openings behaved similarly to the predominant 25 pS openings during DHP and 8Br-cAMP application, with infrequent transitions to and from the predominant level. We conclude that BHK cells provide a useful expression system where the modulations and biophysical aspects of Ca channels can be studied at the single channel level.