Figure 4.

I_heat is activated by calcium released from intracellular stores. (A) Loading cells with the calcium chelator BAPTA reduces I_heat. I_heat was evoked in a neuron by heating to 40°C (Control), then the neuron was exposed to a bath containing 100 μM BAPTA-AM for 5 min at room temperature, BAPTA-AM was washed out of the bath, and the stimulus was reapplied (BAPTA). In this neuron, BAPTA reduced the peak I_heat by 78%. The control response of this neuron also illustrates that in some neurons, I_heat does not return to baseline (broken line) immediately upon cessation of the heat stimulus. (B) Heat stimulates [Ca²⁺]_i increases in the absence of extracellular Ca²⁺. Heating to 40°C caused [Ca²⁺]_i to increase by approximately 200 nM. Removal of Ca²⁺ from the extracellular bath completely blocked Ca²⁺ entry evoked by K⁺ depolarization but the heat-evoked increase in [Ca²⁺]_i persisted.