TY - JOUR
T1 - pH regulatory Na/H exchange by Amphiuma red blood cells
AU - Cala, Peter M
AU - Maldonado, Hector M.
PY - 1994/6
Y1 - 1994/6
N2 - In Amphiuma red blood cells, the Na/H exchanger has been shown to play a central role in the regulation of cell volume following cell shrinkage (Cala, P. M. 1980. Journal of General Physiology. 76:683-708.) The present study was designed to evaluate the existence of pH regulatory Na/H exchange in the Amphiuma red blood cell. The data illustrate that when the intracellular pH(i) was decreased below the normal value of 7.00, Na/H exchange was activated in proportion to the degree of acidification. Once activated, net Na/H exchange flux persisted until normal intracellular pH (6.9-7.0) was restored, with a half time of ≃5 min. These observations established a pH(i) set point of 7.00 for the pH-activated Na/H exchange of Amphiuma red blood cell. This is in contrast to the behavior of osmotically shrunken Amphiuma red blood cells in which no pH(i) set point could be demonstrated. That is, when activated by cell shrinkage the Na/H exchange mediated net Na flux persisted until normal volume was restored regardless of pH(i). In contrast, when activated by cell acidification, the Na/H exchanger functioned until pH(i) was restored to normal and cell volume appeared to have no effect on pH-activated Na/H exchange. Studies evaluating the kinetic and inferentially, the molecular equivalence of the volume and pH(i)-induced Amphiuma erythrocyte Na/H exchanger(s), indicated that the apparent Na affinity of the pH activated cells is four times greater than that of shrunken cells. The apparent V(max) is also higher (two times) in the pH activated cells, suggesting the involvement of two distinct populations of the transporter in pH and volume regulation. However, when analyzed in terms of a bisubstrate model, the same data are consistent with the conclusion that both pH and volume regulatory functions are mediated by the same transport protein. Taken together, these data support the conclusion that volume and pH are regulated by the same effector (Na/H exchanger) under the control of as yet unidentified, distinct and cross inhibitory volume and pH sensing mechanisms.
AB - In Amphiuma red blood cells, the Na/H exchanger has been shown to play a central role in the regulation of cell volume following cell shrinkage (Cala, P. M. 1980. Journal of General Physiology. 76:683-708.) The present study was designed to evaluate the existence of pH regulatory Na/H exchange in the Amphiuma red blood cell. The data illustrate that when the intracellular pH(i) was decreased below the normal value of 7.00, Na/H exchange was activated in proportion to the degree of acidification. Once activated, net Na/H exchange flux persisted until normal intracellular pH (6.9-7.0) was restored, with a half time of ≃5 min. These observations established a pH(i) set point of 7.00 for the pH-activated Na/H exchange of Amphiuma red blood cell. This is in contrast to the behavior of osmotically shrunken Amphiuma red blood cells in which no pH(i) set point could be demonstrated. That is, when activated by cell shrinkage the Na/H exchange mediated net Na flux persisted until normal volume was restored regardless of pH(i). In contrast, when activated by cell acidification, the Na/H exchanger functioned until pH(i) was restored to normal and cell volume appeared to have no effect on pH-activated Na/H exchange. Studies evaluating the kinetic and inferentially, the molecular equivalence of the volume and pH(i)-induced Amphiuma erythrocyte Na/H exchanger(s), indicated that the apparent Na affinity of the pH activated cells is four times greater than that of shrunken cells. The apparent V(max) is also higher (two times) in the pH activated cells, suggesting the involvement of two distinct populations of the transporter in pH and volume regulation. However, when analyzed in terms of a bisubstrate model, the same data are consistent with the conclusion that both pH and volume regulatory functions are mediated by the same transport protein. Taken together, these data support the conclusion that volume and pH are regulated by the same effector (Na/H exchanger) under the control of as yet unidentified, distinct and cross inhibitory volume and pH sensing mechanisms.
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U2 - 10.1085/jgp.103.6.1035
DO - 10.1085/jgp.103.6.1035
M3 - Article
C2 - 7931136
AN - SCOPUS:0028301272
VL - 103
SP - 1035
EP - 1054
JO - Journal of General Physiology
JF - Journal of General Physiology
SN - 0022-1295
IS - 6
ER -