Fig. 6. Temporal responses of grouped recordings of rectal gland artery (RGA) to external Ca²⁺ and Ni²⁺. (A) In calcium-free medium, Ni²⁺ (1 mmoll^-1) promoted Ca²⁺ mobilization; subsequent addition of Ca²⁺ (in the presence of 0.7 mmoll^-1 Ni²⁺) further elevated cytosolic Ca²⁺ levels [Ca²⁺]_i (^*P< 0.01 for Ni²⁺ versus baseline and Ca²⁺ versus Ni²⁺). Values are means ± S.E.M. (N=6). (B) When Ni²⁺ (1.5 mmoll^-1) was added after stimulation of RGA with external Ca²⁺, an inhibitory effect of Ni²⁺ on Ca²⁺ entry was seen (representative recording). Ca²⁺ and Ni²⁺ were added at the times indicated by the arrows.