Carbachol-induced increase in inositol trisphosphate (IP3) content is attenuated by adrenergic stimulation in the isolated working rat heart

Measurement of intracellular calcium of submandibular glands using a high throughput plate reader

Calcium ions (Ca2+) impact nearly every aspect of cellular life and intracellular calcium [Ca2+]i is a critical factor in the regulation of a plethora of physiological functions, including: muscle contraction, saliva secretion, metabolism, gene expression, cell survival and death. By measuring the changes of [Ca2+]i levels, critical physiologic functions can be characterized and aberrant pathologic conditions or drug responses can be efficiently monitored. We developed a protocol for assessment of Ca2+ signaling in the acinar units of submandibular glands isolated from C57BL/6 mice, using benchtop, multi-mode, high throughput plate reader (FlexStation 3). This method represents a powerful tool for unlimited in vitro studies to monitor changes in receptor-mediated Ca2+ responses while retaining functional and morphological features of a native setting.

The interaction of carbachol and strophantin on the electrical and mechanical events in electrically driven strips of guinea pig left atria

We compared the electrophysiological and the mechanical actions of the cholinergic agonist carbachol (CARB) and the digitalis glycoside strophantin (STR) in a study on the electrically driven strips of guinea pig left atria. The respective control values for the resting membrane potential (RMP), action potential amplitude (APA), action potential duration at 20%, 50%, and 90% repolarization levels (APD20,50,90), and time to peak tension (TtPt) were of the order of 61.1 +/- 1.69 nmV, 104.64 +/- 1.28 mV, 28.5 +/- 1.22 msec, 51.0 +/- 1.51 msec, 106.91 +/- 3.81 msec, and 60.1 +/- 1.09 msec. Exposure to CARB (2 x 10(-7) M) rapidly reduced contractility, TtPt, APD, and APA to exceptionally lower levels within the initial 5 minutes and gradually caused a slight hyperpolarization in RMP. Strophantin (1 x 10(-7) M) caused contractility and RMP to increase slightly, APD and APA to reduce less markedly, but did not significantly affect TtPt. Under the influence of combined CARB/STR, the effect of CARB on the contraction amplitude (CA), TtPt, APD, and APA was attenuated and that on RMP was significantly potentiated (p < 0.05), whereas the effects of STR on CA, TtPt, APD, and APA were reversed (p < 0.05), and the effect on RMP was augmented. The action potential duration was less responsive to STR at all depolarization levels with respect to those of CARB and combined CARB/STR. Although the correlation between the time course of APD-20 and APD-90 for STR was poor, the correlation for CARB and combined CARB/STR was highly significant (r > 0.95). The correlation between the effects of CARB on CA and APD-90 was high but poor for the effect of combined CARB/STR. Striking to note is that the rate of induction of contractile changes with CARB (d(delta)/dt = 1.39 +/- 0.05%/sec), and its washout was more rapid (p < 0.05) in comparison to the rate of changes in APD-90 (0.98 +/- 0.05%/sec). This result, however, was not observed with combined CARB/STR. From the results we concluded that CARB and STR act as antagonists when used in combination, with the exception that only the effect on RMP was additive, with asignificant discordance between the rates of induction of effects on CA and APD-90, with the former being more rapid.

Effects of adrenergic and muscarinic agonist stimulation on IP3 and cyclic nucleotide levels in the pressure overloaded rat heart

In this study, the dynamic interrelationships between myocardial functional state and changes in the second messenger content in pressure-overloaded hypertrophied hearts were investigated. Forty-three rat hearts were used after partial clamping of the abdominal aorta. The isolated hearts were perfused with Krebs-Henseleit buffer and allocated to perfusion for 20 s or 40 min as controls (n = 12); or with noradrenaline (10(-6) mol l-1, n = 11); carbachol (3 x 10(-7) mol l-1, n = 9); or noradrenaline plus carbachol (10(-6) mol l-1 + 3 x 10(-7) mol l-1, respectively, n = 11). maxdP/dt increased more than 2-fold already after 20 s on noradrenaline stimulation, followed by a significant increase in cAMP. After 40 min, maxdP/dt was lower than the maximal value, although higher than controls. cAMP was also decreased, but still significantly higher than controls. Perfusion with noradrenaline plus carbachol produced the same changes in maxdP/dt as those seen after noradrenaline stimulation alone, but failed to increase cAMP content after both 20 s and 40 min. The inositol trisphosphate (IP3) content was increased 40 min of control perfusion (p < 0.05). Noradrenaline and carbachol, separately, produced an increase in IP3 content already after 20 s (p < 0.05). The combination of noradrenaline plus carbachol also produced an increase of IP3 (p < 0.05; compared to controls), but to a lesser extent when compared either to noradrenaline or carbachol (p < 0.05). After 40 min of perfusion, IP3 was in the same range regardless of added agonist(s) and still slightly above control level (p < 0.05). The early increase in maxdP/dt induced by noradrenaline or the combination of noradrenaline plus carbachol was not paralleled by a decrease in ATP content. This was also the case upon addition of carbachol alone. However, after 40 min of agonistic perfusion, ATP levels were substantially decreased. In conclusion, myocardial IP3 content in pressure-overloaded hypertrophied hearts was not different from that of sham-operated hearts. After agonistic stimulation, an early increase in IP3 formation was seen. Attenuation of the IP3 response by combined stimulation with noradrenaline and carbachol was initially present in pressure-overloaded hypertrophied hearts. After 40 min no attenuation was found for either IP3 or for cAMP content, suggestive of induction of a desensitization.