Density of muscarinic receptors in rat myocardium during early sepsis.

The muscarinic receptor changes in two subcellular fractions of rat myocardium during sepsis, the sarcolemma (SL) and light vesicles (LV), were studied. [3H]-quinuclidinyl benzilate ([3H]-QNB) was used as a radioligand. Sepsis was induced by cecal ligation and puncture (CLP). The septic rats had higher pulse rates and slightly higher blood glucose levels than control rats. The marker enzyme assays revealed that the SL fraction was enriched with 5'-nucleotidase and the Na(+)-K(+)-ATPase activity increased over 20-fold, while the LV fraction showed very little enrichment when compared with the homogenate. [3H]-QNB binding studies showed that Bmax increased by 58.8% in SL with no changes in LV during early sepsis (9 h post-CLP), but there was no significant change in the Kd value. These data indicate that muscarinic cholinergic receptors in rat heart SL increase during early sepsis. Since the muscarinic cholinergic receptors mediate parasympathetic modulation of myocardial contractility, changes in the number of muscarinic receptors in the cardiac SL may have a pathophysiologic significance in the development of hemodynamic changes during sepsis.