Electrophysiology of the Glands 205 



the Type I submaxillary cells -22 mV. The higher potential in the 

 sublingual cells is presumably because these are not truly resting 

 as this gland is a continuous secretor. It is probably better then to 

 assume that — 22 mV represents a resting potential. Accepting the 

 analyses of Wills and Fenn (1938) the intracellular ion concen- 

 trations in the submaxillary gland are about 115 mEq/kg H 2 for 

 potassium, 47 mEq/kg H 2 for sodium, and 72 mEq/kg H 2 for 

 chloride; other analyses for the sublingual (Lundberg, 1958) and 

 parotid (Burgen, unpublished) give rather similar figures. The 

 equilibrium potentials for the three ions are thus: E K = —90 mV; 

 E Na = +3 2 mV *> E ci = — 1 S mV. The resting potential, there- 

 fore, is quite close to the equilibrium potential for chloride but 

 not to that for either potassium or sodium. Hodgkin and Horo- 

 wicz (1959) have recently shown that in normal skeletal muscle 

 the resting potential appears to be dominated by the potassium 

 concentrations because the intracellular chloride concentration is 

 so low that it can rapidly adjust to changes in the resting potential. 

 If, however, the interior of the muscle is loaded with chloride by 

 soaking the muscle in isotonic potassium chloride for an hour or 

 so, the resting potential then appears to be chloride dominated 

 due to the higher permeability of the membrane for chloride than 

 for potassium. In this state, the resting potential is changed far 

 more by changes in extracellular chloride concentration than by 

 changes in potassium. Because of the high intracellular chloride 

 concentration in the salivary gland, it might be expected that these 

 cells were normally chloride dominated. Burgen and Seeman (1958) 

 have pointed out that since their measurements of sodium and 

 potassium fluxes in the submaxillary gland show an apparent in- 

 crease of at least tenfold during activity while the total membrane 

 conductivity changes at most twofold, the anion contribution must 

 account for at least 90 per cent of the total membrane conductivity. 

 However, if the chloride flux were passive, we should expect that 

 the resting potential of salivary gland cells would be strongly 

 affected by the external chloride concentration. Lundberg (1957c) 

 shows two illustrations of sublingual cells in 160 mEq/1. chloride 

 and then in zero chloride (160 mEq/1. nitrate). The effect of this 

 removal of chloride was to increase the resting potential by only 

 3 mV to 8 mV. If the membrane were passively chloride domin- 

 ated, the potential should decrease and indeed become reversed 

 by at least 50 mV. Therefore, if chloride ions are mainly responsible 



