title: Transport and control of Ca2+ by pigeon erythrocytes. III. A 'paradoxical' expulsion of Ca2+ induced by a low dose of A23187 at 0 degrees C.
abstract: Pigeon erythrocytes expelled preloaded 45Ca2+ in response to a low dose of A23187 at 0 degrees C. We call this phenomenon 'paradoxical' expulsion. Within the first minute, 1.85 +/- 0.38 mumol/l cell water was expelled; after that the internal 45Ca2+ began to rise. The rises in Ca2+ uptake with and without A23187 addition were essentially paralleled. No premonitory rise of 45Ca2+ upon the addition of A23187 was observed. Expulsion of 45Ca2+ in response to A23187 was probably by the action of the Ca2+ pump and not by Na+-Ca2+ exchange since vanadate inhibited, but K+ replacement of Na+ in the medium had no effect. Lysophosphatidylcholine (lysoPC) caused an abrupt increase in 45Ca2+ influx by cells at 0 degrees C and was dose dependent. However, a very low dose of lysoPC induced expulsion of preloaded 45Ca2+ similar to that by A23187, the response was fast and transitory, without any premonitory rise in 45Ca2+ uptake. The results lend support to the suggestion that the signal to which cells respond may be a sudden change in Ca2+ influx per se rather than a change in internal Ca2+ concentration. These features of 'paradoxical' 45Ca2+ expulsion induced by A23187 and lysoPC are not expected from mass-action equilibria but, instead, agree with the characteristics of an energy-dissipating control mechanism.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology*; D002118:Calcium / Q000097:blood*; D002132:Calcium Radioisotopes; D010856:Columbidae / Q000097:blood; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism; D007700:Kinetics; D008244:Lysophosphatidylcholines / Q000494:pharmacology; D014638:Vanadates / Q000494:pharmacology
chemical_list: D002132:Calcium Radioisotopes; D007473:Ion Channels; D008244:Lysophosphatidylcholines; D000001:Calcimycin; D014638:Vanadates; D002118:Calcium