The cholinergic agonist carbachol produces a concentration-dependent (half-maximum inhibitory concentration = 0.9 μM) decrease in the Na+-K+-adenosine triphosphatase (ATPase) activity of rabbit cardiac sarcolemma that occurred only in the presence of guanosine 5'-[γ-thio]triphosphate (0.1 μM GTPγS) and reached 40% inhibition. The inhibition is blocked by the muscarinic receptor antagonist atropine (10 μM) and is abolished in sarcolemma treated with pertussis toxin (20 μg/ml) in the presence of 100 μM NAD. GTPγS alone reduces Na+-K+-ATPase activity by 45% (half-maximum inhibitory = 1 μM). The apparent affinity of the enzyme for GTPγS is increased ~ 10-fold in the presence of 1 μM carbachol. In sarcolemma solubilized with the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS, 10 mM), the GTPγS-dependent inhibition of the Na+-K+-ATPase is also observed. Gel filtration of a CHAPS extract of sarcolemma on a Sepharose CL-6B column resulted in a separation of Na+-K+-ATPase and pertussis toxin-sensitive G(I) activities. Na+-K+-ATPase activity that was separated on the column lost its sensitivity to the inhibitory action of guanine nucleotides. Inhibitory effects (20-30%) of guanosine 5'-triphosphate analogues [Gpp(NH)p, GTPγS, or Gpp(CH2)p] at micromolar concentrations were restored when the Na+-K+-ATPase activity was recombined with fractions that contained the pertussis toxin-sensitive G(i) protein(s). Similar concentrations of guanosine 5'-triphosphate, guanosine 5'-diphosphate, guanosine-5'-[β-thio]diphosphate, or App(NH)p were unable to induce the G(i) protein-mediated attenuation of Na+-K+-ATPase activity in the reconstitution system. These results suggest that a pertussis toxin-sensitive G(i) protein may act as a transducer of the inhibitory hormonal signals on Na+-K+-ATPase in the sarcolemma.
|Number of pages||5|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|Issue number||4 SUPPL.|
|State||Published - 1 Jan 1991|
- cardiac sarcolemma