AN ELECTROPHYSIOLOGICAL STUDY OF RED CHROMATOPHORE OF PRAWN PALAEMONETES - OBSERVATIONS ON ACTION OF RED PIGMENT-CONCENTRATING HORMONE

1. 1. The resting potential of the prawn red chromatophore is a function of the external potassium concentration and was observed to be 55 ±15 mV inside negative. 2. 2. The isosmotic addition of potassium ion to the bathing medium induces a calculated shrinkage of a pigment-containing compartment of 40 per cent per tenfold change in [K+]out. 3. 3. An approximate internal potassium level of 200 mequiv./1 is predicted from electrochemical equations. 4. 4. The effective resistance (Reff) of the chromatophore is 1·1× 105 ohms. 5. 5. These chromatophores are electronically coupled. The true membrane resistance (Rm) is therefore somewhat higher than Reff. 6. 6. Red pigment-containing hormone causes membrane hyperpolarization, the magnitude of which is a function of the amount of pigment concentration that occurs. No major change in ion permeability occurs during the period of response. © 1968.