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1. The Ca-sensitive photoprotein aequorin was injected into squid axons and the light response to stimulation or depolarizing voltage clamp pulses recorded.

2. The effects of Mn²⁺, Co²⁺, Ni²⁺, La³⁺ and of the organic Ca antagonists D-600 and iproveratril on the early tetrodotoxin-sensitive and late tetrodotoxin-insensitive components of the light response were studied.

3. The late tetrodotoxin-insensitive component can be blocked, reversibly, by concentrations of Mn, Co and Ni that reduce but do not block the tetrodotoxin-sensitive component. The late component can also be blocked by La³⁺ and the organic Ca antagonists D-600 and iproveratril.

4. Mn²⁺, Co²⁺, Ni²⁺ and the drug D-600 all reduce the Na currents, but have little effect on either outward or inward K currents. Tetraethylammonium blocks the outward K current but has no appreciable effect on the tetrodotoxin-insensitive entry of Ca.

5. Concentrations of Mn between 5 and 50 mM substantially reduce the light output during a train of action potentials; they also slightly reduce the rate of rise of the action potential.

6. On pharmacological grounds it is concluded that the tetrodotoxin-insensitive component of Ca entry does not represent Ca ions passing through the K permeability channels. There must exist a potential-dependent late Ca channel that is distinct from the well known Na and K channels of the action potential. A possible function for this late Ca channel in the coupling of excitation to secretion is discussed.

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				S. Meis and H.-C. Pape Properties of a Ca2+-Activated K+ Conductance in Acutely Isolated Pyramidal-Like Neurons From the Rat Basolateral Amygdaloid Complex J Neurophysiol, September 1, 1997; 78(3): 1256 - 1262. [Abstract] [Full Text] [PDF]