High plasma buffering and the absence of a red blood cell beta-NHE response in brown bullhead (Ameiurus nebulosus).

The high non-bicarbonate buffer capacity of brown bullhead (Ameiurus nebulosus) plasma was postulated to function as an alternative mechanism for the protection of red blood cell (RBC) intracellular pH (pHi) in the absence or attenuation of a RBC adrenergic response. The requirement for protecting RBC pHi arises from the presence of a Root effect haemoglobin in bullhead. In support of this hypothesis, bullhead RBCs incubated in vitro with isoproterenol (10(-8)-10(-5) mol l(-1)) or forskolin (10(-4) mol l(-1)) exhibited significant cyclic AMP accumulation, but failed to exhibit cell swelling or significant Na(+) or Cl(-) accumulation; plasma pH (pHe) was also unaffected. Similarly, no significant effect on RBC water content, Na(+) or Cl(-) concentration, or pHe was detected in bullhead blood incubated with 8-bromo cyclic AMP (10(-4)-10(-2) mol l(-1)) in vitro. These results suggest that while bullhead RBCs possess a beta-adrenoreceptor linked to cyclic AMP formation, stimulation of this adrenergic receptor does not result in measurable activation of a Na(+)/H(+) exchanger.