Decrease in the Sensitivity of Myocardium to M3 Muscarinic Receptor Stimulation during Postnatal Ontogenisis

Abstract

Type 3 muscarinic receptors (M3 receptors) participate in the mediation of cholinergic effects in mammalian myocardium, along with M2 receptors. However, myocardium of adult mammals demonstrates only modest electrophysiological effects in response to selective stimulation of M3 receptors which are hardly comparable to the effects produced by M2 stimulation. In the present study, the effects of selective M3 stimulation induced by application of the muscarinic agonist pilocarpine (10 μM) in the presence of the selective M2 blocker methoctramine (100 nM) on the action potential (AP) waveform were investigated in isolated atrial and ventricular preparations from newborn and 3-week-old rats and compared to those in preparations from adult rats. In the atrial myocardium, stimulation of M3 receptors produced a comparable reduction of AP duration in newborn and adult rats, while in 3-week-old rats the effect was negligible. In ventricular myocardial preparations from newborn rats, the effect of M3 stimulation was more than 3 times stronger compared to that from adult rats, while preparations from 3-week old rats demonstrated no definite effect, similarly to atrial preparations. In all studied types of cardiac preparations, the effects of M3 stimulation were eliminated by the selective M3 antagonist 4-DAMP (10 nM). The results of RT-PCR show that the amount of product of the M3 receptor gene decreases with the maturation of animals both in atrial and ventricular myocardium. We concluded that the contribution of M3 receptors to the mediation of cardiac cholinergic responses decreases during postnatal ontogenesis. These age-related changes may be associated with downregulation of M3 receptor gene expression.

The role of M3 receptors in regulation of electrical activity deteriorates in the rat heart during ageing

“…In the present study we demonstrate the marked changes in receptor mechanism of muscarinic agonist effects on rat cardiac electrophysiology associated with ageing. Previously, age-related decrease in contribution of M3 receptors to the mediation of cholinergic changes in AP morphology was shown in hearts of rats during early postnatal ontogenesis ( Tapilina and Abramochkin, 2016 ). The same study demonstrates a decrease in M3 gene expression in rat atrial and ventricular myocardium associated with maturation.…”

“…It is likely that muscarinic receptors in ventricular myocytes are damaged during the enzymatic isolation. Since their expression in ventricular myocardium is lower than in atrial ( Hellgre et al, 2000 ; Tapilina and Abramochkin, 2016 ), it is not surprising that the effect of M3 stimulation disappears after isolation of single myocytes.…”

“…Molecular mechanisms of cardiac ageing are complex and still not well understood. Recently, our group has demonstrated drastic down-regulation of M3 receptors expression and their functional significance in rat myocardium during early postnatal ontogenesis ( Tapilina and Abramochkin, 2016 ). Moreover, a decrease in expression of M3 receptors has been shown in mouse model of cardiac ageing ( Wang et al, 2018 ).…”

Extracellular ATP and β-NAD alter electrical properties and cholinergic effects in the rat heart in age-specific manner

“…Action potentials were recorded from all types of multicellular preparations with sharp glass microelectrodes (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) filled with 3 M KCl and connected to a high input impedance amplifier Model 1600 (A-MSystems, Sequim, WA, USA). The signal was digitized and analyzed using specific hardware (E-154 analog-to-digital converter, L-card, Moscow, Russia, www.lcard.ru) and software (PowerGraph 3.3, DISoft, Russia, www.powergraph.ru/en).…”

“…Gq-coupled signaling is involved in many pathways of heart regulation, including inhibitory effect of M3 cholinoreceptors stimulation by ACh [41,42], which is more prominent in neonatal than adult rat myocardium [43]. Also, it has been demonstrated in cardiomyocytes from neonate rats that P2Y1 receptors are expressed at higher level than P2Y2 and P2Y4 [18].…”