Osmotic properties of internally perfused barnacle muscle cells. I. Isosmotic conditions

Barnacle muscle cells regulate their volume when exposed to anisotonic cond itions. Due to their large size, these cells can be internally perfused. In terestingly, perfused cells maintain their volume regulatory properties (17 ,21). Thus, the osmotic properties of barnacle muscle cells can be studied under conditions in which the intracellular and extracellular osmolalities, the membrane potential (V-M), the cell volume and the intracellular pressu re can all be measured simultaneously. In this manuscript we report the eff ect that various rates of isosmotic (1000 mOsm.kg H2O-1) intracellular perf usion have on Cell Volume, intracellular pressure, intracellular osmolality , V-M, and the apparent sarcolemmal hydraulic water permeability (L'(p)). R eplacement of the cytosol with the perfusate at a perfusion rate of 0.83 mu l.min(-1) took 120 min. During this transition period, the cell volume incr eased from 45.1 +/-6.9 mul to 73.7 +/-5.8 mul, the intracellular osmolality decreased from 1406 +/- 133 to 1188 +/- 64 mOsm.kg H2O-1, and the intracel lular pressure underwent a transient drop of 2.8 cm H2O. After 2.5 hr of co ntinuous perfusion at 0.83 mul.min(-1), the above mentioned parameters reac hed steady values: the L'(p) was 1.35 x 10(5) cm.sec(-1).Osm(-1).kg H2O-1; cell volume was 67.2 +/-6 mul; die intracellular osmolality was 1052 +/- 10 mOsm.kg H2O-1; the intracellular pressure was 5.6 +/-0.4 cm H2O; V-M depol arized slowly at a rate of 0.03 mV.min(-1). Stepwise increases in the rate of perfusion (from 0.83 to 3.18 mul min(-1)) produced reversible increases in the intracellular pressure, Up and cell volume and decreases in intracel lular osmolality. We conclude that intracellular perfusion: i/produces a tr ansient removal of intracellular osmotically active components; ii/promotes sarcolemmal water filtration; iii/induces a laminar flow of perfusate at t he center of the cell, and iv/enables calculations of sarcolemmal Up values under isosmotic conditions.