Calcium regulation in blowflies: absence of a role for midgut

Adult blowflies (Calliphora vicina) survive many days without increased mortality if fed 12.5 mM CaCl2 solution in place of water. Initially the calcium content of these flies rapidly increases to more than double the original content but then remains stable for many days afterward. Calcium absorption continues at a similar rate throughout this time. Midguts isolated from flies fed either 12.5 mM CaCl2 solution or distilled water have the same capacity to absorb calcium. Dopamine, octopamine, proctolin, and 5-hydroxytryptamine, at pharmacological doses, do not affect calcium absorption by the isolated midgut. Malpighian tubules are the site of most rapid calcium turnover when flies are fed excess calcium. It is concluded that excretion and not absorption is the major site of hemolymph calcium regulation in C. vicina. This contrasts to the situation in mammals where transcellular calcium absorption by the duodenum is precisely controlled. It is suggested that to avoid high luminal calcium concentrations, fast calcium absorption from the blowfly midgut is adapted to remove calcium from the lumen rather than to regulate hemolymph calcium concentration.