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

Figures

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  Fig. 1. Effects of pilocarpine on AP waveform in rat right atrial preparations. (a,b,c) Original traces of APs recorded under the effect of 10-5M pilocarpine alone and in the presence of 10-7M AQ-RA 741 (selective stimulation of M3 receptors) in right atrial preparations from young (a), adult (b) and ageing (c) rats. AP traces are superimposed on respective control traces, which were recorded right before pilocarpine application. (d) Relative changes of AP duration at 90% repolarization level induced by 10-5M pilocarpine alone or in the presence of M2 and M3 blockers, expressed in % of control AP duration. * - significant reduction of APD, p < 0.05, paired t-test. & - significant difference from 4 months old rats, p < 0.05, two-way ANOVA with further Tukey's post hoc multiple comparisons.

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  Fig. 2. Effects of pilocarpine on AP duration in rat right ventricular wall preparations. (a,b,c) Original traces of APs recorded under the effect of 10-5M pilocarpine alone and in the presence of 10-7M AQ-RA 741 (selective stimulation of M3 receptors) in right ventricular wall preparations from young (a), adult (b) and ageing (c) rats. AP traces are superimposed with respective control traces, which were recorded right before pilocarpine application. (d) Relative changes of AP duration at 90% repolarization level induced by 10-5M pilocarpine alone or in the presence of M2 and M3 blockers, expressed in % of control AP duration. * - significant reduction of APD, p < 0.05, paired t-test. No significant differences between 3 age groups of rats were detected by two-way ANOVA with further Tukey's post hoc multiple comparisons.

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  Fig. 3. Effects of selective M3-stimulation on the L-type calcium current (ICaL) in rat atrial myocytes. (a-c) Original tracings of ICaL induced by depolarization to 0 mV, from 3 different representative experiments recorded in the presence of M2 blocker AQ-RA 741 before and during the application of 10-5M pilocarpine. (d-f) Comparison of I–V curves of ICaL recorded in atrial myocytes from young (d), adult (e) and ageing (f) rats before and during the application of pilocarpine in the presence of AQ-RA 741. ICaL I–V curves recorded under the effect of pilocarpine without M2 blocker are also provided. (g) relative reduction of peak ICaL amplitude at 0 mV in myocytes from 3 age groups of rats, induced by 10-5M pilocarpine alone, in the presence of M2 blocker or combination of M2 and M3 blockers. The results are presented as means ± S.E.M. of 11–15 myocytes (n stated on the figure) from 4 rats. The current was elicited using protocol with 2-step square-pulse depolarization from the holding potential of −80 mV to −40 mV (first step for inactivation of INa) and further to −30 - +40 mV with 10 mV increment. The current amplitude was calculated as the difference between the peak ICaL and the…

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  Fig. 4. Relative transcription level of M3 receptor gene in atrial (a) and ventricular (b) myocardium of rats from 3 age groups (n = 6 in each group). The y-axis shows the relative amount of mRNA in the samples, calculated from the results of RT-PCR. Results are normalized to the level of transcription of GAPDH gene. The results are shown in arbitrary units. * and ** - significant difference from young rats, one-way ANOVA, p < 0.05 and p < 0.01, respectively.