Abstract
AbstractThe effects of hypercapnia were studied in cat papillary muscles driven at a frequency of 12 beats/min. The Pco2 of the medium was changed from ⋍ 25 mm to 95 mmHg. Developed tension (DT) and maximal rate of tension development (dT/dt max) were recorded during a 30-minute period. Under isometric conditions and at 30 °C, increasing Pco2 resulted in a biphasic phenomenon Characterized by a decrease in DT and dT/dt max, followed by a partial recovery. Similar results were obtained under isotonic conditions, reserpine pretreatment or addition of propranolol. In the latter experiments, however, values of maximum depression and after 30 minutes of hypercapnia, were significantly lower than without the β-blocking agent.At 22 °C and 22 °C plus reserpine, maximum contractility depression was greater and occurred later during the hypercapnic period than at 30 °C. In addition, at 22 °C plus reserpine, the degree and rate of recovery were significantly lower than at 30 °C.High calcium concentration diminished ...
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