Which preconditioning‐associated G protein‐coupled receptors are expressed on the sarcolemma?

Abstract

It has been assumed that G protein‐coupled receptors associated with preconditioning reside on the sarcolemma. We tested that assumption by infecting rabbit ventricular myocytes with adenovirus encoding cyclic nucleotide‐gated channels. Increasing cAMP opens the channel and increases ionic currents measured using whole cell patch clamp. Peak current was determined by exposure of cells to a phosphodiesterase inhibitor cocktail (PDEI) plus 50nM isoproterenol (ISO) at end of experiments. Current after 50nM ISO binding to Gs‐coupled β‐adrenergic receptors was 56±9% of peak. 500nM Bradykinin or 20nM δ‐opioid agonist DADLE reduced ISO current to 19±5 and 11±3% of peak, respectively, indicating activation of these Gi‐coupled receptors. 200nM CCPA and 200nM IB‐MECA, adenosine A1 and A3 agonists, respectively, also attenuated responses to ISO with maximal currents of 25±11% and 24±5% of peak. A2 subtypes are normally Gs‐coupled. Neither 1μM BAY60‐6583, A2b agonist, nor 300nM CGS21680, A2a agonist, increased current themselves, but CGS21680 could after PDEI indicating a low level of A2a. Neither attenuated ISO's current. We conclude that all four Gi‐coupled receptors and the Gs‐coupled A2a are present but not A2b. If there really is a role for the A2b in preconditioning's protection, then the signaling must involve a different cell type in the heart such as vascular smooth muscle. HL‐20648, HL‐74278