Transport and control of Ca2+ by pigeon erythrocytes. II. Evidence against a simple feedback control of cell Ca2+ and evidence for the involvement of more than one pool.

Pigeon erythrocytes did not behave as expected from simple feedback mechanisms. The pool size for exchangeable cell Ca2+ was approximately proportional to the A23187-induced apparent 45Ca2+ influx ("J(in,app)") from 0.4 to 14 mumoles/min X l cell water at 184 microM external [Ca2+]. From earlier data, total cell 45Ca2+ was approximately proportional to J(in,app) from 10 to 120 mumoles/l X min. Thus there was no influx range where cell 45Ca2+ was held approximately constant. External [Ca2+] affected Ca2+ pool size independently of its effect of J(in,app). Trifluoperazine did not increase cell 45Ca2+ with or without A23187. In the presence of A23187, 45Ca2+ entered a pool early in the incubation which later became inaccessible to 45Ca2+ entry and exit. Lysolecithin addition produced an abrupt rise in cell 45Ca2+, much of which occupied a pool that quickly became inaccessible. The increased 45Ca2+ influx induced by lysolecithin dropped quickly and markedly with time. It is hard to explain inaccessible pool(s), especially in the presence of A23187 by membrane-bounded compartments. We suggest that nonexchangeable 45Ca2+ might be held by an energy-dependent binding protein(s).