Mechanisms of pHi recovery from NH4Cl-induced acidosis in anoxic isolated turtle heart: a 31P-NMR study.

Mechanisms of intracellular pH (pHi) recovery from NH4Cl-induced acidosis were investigated on isolated perfused hearts of the turtle, Chrysemys picta bellii, using 31P nuclear magnetic resonance (NMR) spectroscopy at 20 degrees C. A major goal was to assess the activity of these mechanisms under anoxic conditions. Based on calculated buffer capacity and a pHi recovery range at 20 degrees C of 6.75-6.95 (normal pHi 7.2-7.4), mean H' efflux rate during perfusion with CO2-free N-tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid (TES)-buffered Ringer was only 15% (normoxia) and 25% (anoxia) of that with HCO3-buffered Ringer. With HCO3 solution, anoxic H1 efflux rate was approximately 50% of normoxia (0.333 vs. 0.645 mmol.l-1.min-1), but in TES solution, H1 efflux rate was unaffected by anoxia. To further characterize the transporters, we used blockers [the Na(+)-H+ antiport inhibitor 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) and the anion exchanger inhibitor 4,4'diisothiocyanostilbene-2, 2'-disulfonic acid (DIDS)], ion substitution, and temperature change. EIPA (10 microM) inhibited H+ efflux rate by 40% in anoxic TES solution; DIDS (0.5 mM) blocked H+ efflux rate by 85% in anoxic HCO3 solution. No pHi recovery was observed in either normoxic or anoxic Na(+)-free solutions, but normal recovery was observed in the absence of extracellular Cl-. Recovery of pHi occurred 2-3 times faster at 30 degrees C than at 20 degrees C. ATP was unaffected by any manipulation in this study, whereas creatine phosphate (CP) fell during anoxia, and both CP and mechanical performance changed in parallel to pHi. We conclude that pHi regulation functions during anoxia, although at a reduced rate, and that recovery from acidosis is dominated, during both normoxia and anoxia, by a DIDS-sensitive Na+ and HCO3(-)-dependent mechanism, whereas EIPA-sensitive Na(+)-H+ antiport plays a less important role.

Acid-base balance and temperature in a predominantly skin-breathing salamander, Cryptobranchus alleganiensis.

Blood gases and pH and plasma [Na+], [K+], [Cl-] and [lactate] were measured on arterial blood of the large predominantly skin-breathing salamander, the hellbender (Cryptobranchus alleganiensis), at 5, 15 and 25 degrees C, both with and without access to air. Access to air had no effect of any of the acid-base variables, but temperature had significant effects on both pH and PCO2. Blood pH decreased with temperature by about 0.016 unit/degrees C both in vivo and in vitro (over the range studied) which is similar to the change previously observed on other ectotherms. Blood PCO2 rose significantly with temperature while plasma [HCO-3] rose slightly but insignificantly. Other ions were unaffected by temperature. This is the first demonstration that the characteristics ectothermic acid-base response to temperature occurs in a vertebrate respiring exclusively through its skin. We suggest that the response in this animal is essentially passive and uncontrolled and is due to: (1) the proportional effects of temperature upon metabolic CO2 production and blood PCO2, and (2) the temperature-independent CO2 conductance of the skin.

Skin circulation of the frog, Rana catesbeiana: distribution and dynamics.

The volume and distribution of blood flow to the skin of the bullfrog, Rana catesbeiana, from both the pulmocutaneous and systemic arterial sources were measured. Radioactively labelled microspheres (35 +/- 5 micron) were used to map the regional distribution of each of these sources and to measure the systemic blood flow to the skin during air breathing and diving. Cutaneous artery blood flow was measured with an ultrasonic (Doppler) flowmeter. The systemic supply to the skin perfuses predominantly the limbs, while the largest cutaneous artery supply is to the back and flanks of the animal. All regions received blood from both sources. The cutaneous artery blood flow decreased during diving to approximately one-third of the pre-dive level. This decrease, however, was offset by an approximately equivalent increase in systemic blood flow to the skin during diving. These data should reconcile the decrease in pulmocutaneous blood flow and the important function of the skin as a gas exchanger during diving.

Microsphere studies of bullfrog central vascular shunts during diving and breathing in air.

Bidirectional central vascular shunts were measured during diving and breathing in air in unanesthetized bullfrogs by using pulmonary trapping of 38 mu mean diameter radionuclide-labelled microspheres. Six animals studied during diving exhibited a strong overall right-to-left shunting pattern comprised of both a predominant (68% mean) right-to-left shunt and a weak (23%) left-to-right countershunt. Five animals with access to air showed a variety of distribution patterns, including predominant shunts in the left-to-right (1 animal) and right-to-left (1 animal) directions, nearly complete mixing (2 animals) and separation of systemic and pulmonary venous returns (1 animal).