The effects of atenolol (2-5 mmol/l), sotalol (1-2 mmol/l) and pamatolol (0.1-1 mmol/l), together with N-tertiary butyl phenoxypropanolamines with o-methyl (D-2T: 50-100 mumol/l) m-methyl (D-3T: 50-100 mumol/l) and p-methyl (D-4T: 100-200 mumol/l) group as well as with o,p-methyl groups (D-24T) (50-100 mumol/l) on action potentials (APs) were investigated in isolated guinea-pig papillary muscles. All the drugs in these concentrations produced a concentration-dependent reduction of the maximum upstroke velocity (Vmax). The reduction of Vmax in premature APs induced by stimuli interpolated between the basic driving rate of 0.25, 0.1 or 0.027 Hz decayed exponentially during diastolic intervals. The time constants of these decay processes tau for atenolol, pamatolol and sotalol ranged between 260-541 ms, those for D-3T and D-4T between 655-1,166 ms, and D-2T and D-24T between 1,565-1,931 ms. A drug which provided larger tau values caused the reduction of Vmax in a wider range of the frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
The effects of bucumolol (BUC), nadolol (NAD) and nifenalol (NIF) on contractile forces and on action potentials (APs) were investigated in isolated guinea pig atrial and papillary muscles, respectively. Log 1/ED40 values for the negative inotropic effects of these drugs were 0.097, 10 and 0.74 mmol/l in this order. BUC (50 mumol/l), NAD (0.5 mmol/l) and NIF (0.2 mmol/l) produced about 60, 20 and 20% reduction of Vmax at 1 Hz. The frequency-dependent reductions at these and higher concentrations were greatest for BUC, intermediate for NAD and least for NIF. These potencies at certain frequencies were, as a whole, consistent with log P-potency relationship established in our previous papers (Harada et al. 1981; Ban et al. 1985). The reductions of Vmax in APs in response to premature stimuli during basic stimuli at the rate of 0.25 or 0.027 Hz decayed exponentially during diastolic intervals (DI). The time constants of these decay process (tau) estimated by linear and nonlinear regression analyses and by eye were 12.2-9.6 s for BUC (50-100 mumol/l) and 2.9-4.8 s for NAD (1-2 mmol/l) and 57-87 ms for NIF (0.2-1 mmol/l). In terms of the molecular weight (MW)-log tau relationship (Ban et al. 1985), these tau values are within the 95% fiducial limit for BUC and NAD and deviated from the lower fiducial limit for NIF. The frequency-dependent reductions of Vmax by these drugs were explained in terms of a function of tau and the intercept Ao. Based on the study made by Cohen et al.(ABSTRACT TRUNCATED AT 250 WORDS)
In order to assess the effects of Bay-K-8644 on electrical activities of young embryonic chick hearts in which the rising phase of the action potential (AP) depends on tetrodotoxin-insensitive slow Na+ currents, slow AP were recorded in spontaneously beating 3-day-old embryonic chick hearts. Bay-K-8644(10(-6) mol/l) caused increases in the maximum rate of rise, amplitude, and duration of the slow AP; there was a slow increase in the spontaneous firing rate. Thus, Bay-K-8644 stimulates Na+ influx through TTX-insensitive slow channels.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.