Mechanisms of calcium absorption by anterior and posterior segments of the intestinal tract of juvenile lake sturgeon

Abstract

Rapid growth in juvenile fish increases calcium demand, and the intestine may play a role in calcium homeostasis at this life stage, in addition to branchial and renal transport. This study examined calcium flux in the gastrointestinal tract (GIT) of freshwater juvenile lake sturgeon acclimated to 0.14, 0.34, and 2.26mmolL−1 environmental calcium. Net Ca2+ flux did not differ due to environmental [Ca2+] in either the anterior or posterior intestine. Blocking the apical epithelial calcium channel (ECaC) with ruthenium red (RR, 8.5μmolL−1) significantly decreased Ca2+ influx in the anterior intestine, but exposure to the plasma membrane Ca2+-ATP-ase (PMCA) inhibitor trifluoperazine (TFP, 10mmolL−1) had no effect at any environmental [Ca2+], nor did inhibition of the Na+–Ca2+ exchanger (NCX) with KB-R7943 (10μmolL−1). Neither RR nor TFP affected Ca2+ uptake by the posterior intestine in any of the treatment groups, but KB-R7943 reduced net calcium flux in the posterior intestine at all environmental [Ca2+]. Thus, basolateral Ca2+ influx in the posterior GIT of lake sturgeon relies more heavily on NCX than PMCA. Furthermore, the differing pharmacological effects in the anterior and posterior intestine suggest that the dominant transporters responsible for calcium uptake vary over the length of the GIT in lake sturgeon.