8. Biscoe TJ, Purves MJ, Sampson SR: The frequency of nerve impulses in single carotid body chemoreceptor afferent fibres recorded in vivo with intact circulation. J Physiol (Lond) 208: 121-131, 1970 9. Hilton SM-Inhibition of barorcceptor reflexes on hypothalamic stimulation (absxr). J Physiol (Lond) 165: 56P, 1963 10. GebberGL, Snyder DW: Hypothalamic control of baroreceptor reflexes. Am J Physiol 218: 124-131. 1970 11. Hockman CH, Talesnik J, Livingston HE Central nervous system modulation

more »

... baroreceptor reflexes. AmJ Physiol217: 1681-1689, 1969 12. Humphreys PW, Joels N, McAllen RM. Modification of the*reflex response to stimulation of carotid sinus baroreceptors during and following stimulation of the hypothalamic defence area in the cat J Physiol (Lond) 216: 461-482, 1971 13. Klevans LR, Gebber GL: Facihtatory forcbrain influence on cardiac component of baroreceptor reflexes. Am J Physiol 219: 1235-1241, 1970 14. Spyer KM: Baroreceptor sensitive neurons in the anterior hypothalamus of the cat. J Physiol (Lond) 224: 245-257, 1972 15. Thomas MR, Calaresu FR: Responses of single units in the medical hypothalamus to electrical stimulation of the carotid sinus nerve in the cat. Brain Res 44: 49-62, 1972 16. Chai CY, Share NN, Wang SC: Central control of sympathetic cardiac augmentation in lower brainstcm of the cat. Am J Physiol 202: 25-30, 1962 17. Doba N, Reis DJ: Acute fulminating neurogenic hypertension produced by brainstem lesions in the rat. Ore SUMMARY The effects of quinidine and temperature on Na influx and contraction frequency of synchronously contracting rat myocardia! cells in mooolayer cultures were studied. Quinidine (10~* M to 10 a M) produced a prompt reduction in Na influx, maximum after 30 seconds of exposure, and dose-dependent along a sigmoid log dose-response curve. At 37°C, Na influx (/imol/10" cells per sec) decreased from 30.19 to 24.70 (/> < 0.001)and 10.49(/> < O.OODon exposure to quinidine, 10~6 and 10 -i M, respectively. Simultaneously the contraction frequency decreased from a control of 120/min to 105/min and 48/min with 1 0 * M and S x 1 0 ' M quinidine. At higher concentrations spontaneous contractions ceased. The effects on Na influx and contraction were reversible by washing the cells free of the drug (30 seconds). A temperature-dependent decrease by guest on July 23, 2018 http://circres.ahajournals.org/ Downloaded from D McCall cultured rat myocardial cells. Effect of quinidine and temperature on sodium uptake and contraction frequency of