The American journal of physiology
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It has been established that H+ secretion can be maintained in frog stomach in the absence of exogenous CO2 by using a nutrient bathing fluid containing 25 mM H2PO4 (pH approximately equal to 4.5) or by lowering the pH of a nonbuffered nutrient solution to about 3.0-3.6. Exogenous CO2 in the presence of these nutrient solutions uniformly caused a marked decrease in H+ secretion, PD, adn short-circuit current (Isc) and an increase in transmucosal resistance (R). Elevation of nutrient [k+] to 83 mM reduced R significantly but transiently without change in H+ when nutrient pH less than 5.0, whereas R returned to base line and H+ increased when nutrient pH greater than 5.0. ⋯ Removal of exogenous CO2 from standard bicarbonate nutrient solution reduced by 50% the H+, PD, and Isc without change in R; K+-free nutrient solutions reverse these changes in Isc and PD but not in H+. The dropping PD and rising R induced by K+-free nutrient solutions in 5% CO2 - 95% O2 are returned toward normal by 100% O2. Our findings support an important role for exogenous CO2 in maintaining normal acid-base balance in frog mucosa by acting as an acidifying agent.
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Coronary vascular and myocardial responses to selective hypoxic and/or hypercapnic carotid chemoreceptor stimulation were investigated in constantly ventilated, pentobarbital or urethan-chloralose anesthetized dogs. Bilaterally isolated carotid chemoreceptors were perfused with autologous blood of varying O2 and CO2 tensions via an extracorporeal lung circuit. Systemic gas tensions were unchanged. ⋯ These studies show that local carotid body stimulation increases coronary blood flow but has little effect on the myocardium. The increase in coronary blood flow results mainly from an increase in systemic arterial pressure. Thus these data provide little evidence for increased sympathetic activity of the heart during local stimulation of the carotid chemoreceptors with hypoxic and hypercapnic blood.
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Effects of sodium nitrate were compared with sodium chloride loading on transport of electrolytes by the nephron. Maximal levels of free water clearance/clomerular filtration rate (CH2O/GFR) averaged 8.4% with nitrate loading and 14.4% with saline loading. Since ethacrynic acid and chlorothiazide exert their major natriuretic effect in the distal nephron, the increment in Na ad Cl reabsorbed beyond the proximal tubule. ⋯ At every level of UNaV, fractional bicarbonate reabsorption was higher, urine pH was lower, and urinary potassium excretion (UKV) was higher in the nitrate studies. Thus, compared with saline loading, sodium nitrate decreases chloride and sodium reabsorption in the distal nephron. The higher hydrogen and potassium secretion in the nitrate studies may be consequent to the decreased ability of the distal nephron to reabsorb chloride.
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The effects of pH variation on ionic exchange and mechanical function were studied in the arterially perfused rat and rabbit septa. The pH and PCO2 of the control perfusate were 7.40 and 39 mmHg, respectively. In the rabbit septum a metabolic acidosis (pH equals 6.82, PCO2 equals 39 mmHg) caused a loss of 16% of control tension in 12 min. ⋯ The net gain could not be mimicked by epinephrine administration or blocked by propranolol and was absent in the beating rat septum and the quiescent rabbit septum. These results suggest that the net uptake of K+, which appears to be dependent on a period of depolarization, and the changes of contractility are controlled by the H+ ion concentration at a cellular site whose exchange with the extracellular space is characterized by a considerable restriction of diffusion. Changes of contractility are not related to the net uptake of K+.