Alpha-subunit of Gs directly activates cardiac calcium channels in lipid bilayers

Specific guanine nucleotide-binding proteins (G proteins) couple receptors to calcium channels indirectly via cytoplasmic agents such as protein kinases (Birnbaumer et al., Kidney Int. 32: 514-537, 1987). Direct coupling between the stimulatory G protein from adenylyl cyclase (Gs) and calcium channels has been shown recently in inside-out cell-free membrane patches excised from guinea pig myocytes, i.e., in the absence of cytoplasm (Yatani et al., Science Wash. DC 238: 1288-1292, 1987). In these patches, single calcium channel currents were unstable, and this complicated both the experiments and their interpretation. Calcium currents are more stable when calcium channels are incorporated into planar lipid bilayers (Rosenberg et al., Science Wash. DC 231: 1564-1566, 1986), and consequently, we used the latter method to examine the direct coupling hypothesis more fully. Bovine cardiac sarcolemmal vesicles were added to the cis side of a chamber divided by a preformed planar lipid bilayer. The cytoplasmic surface faced the trans chamber and was bathed by an ATP-free minimal solution. The extracellular solution in the cis chamber contained 100 mM Ba2+, and both chambers contained the dihydropyridine agonist BAY K 8644 at 1 microM.(ABSTRACT TRUNCATED AT 250 WORDS)