Membrane potentials of human fibroblast strains in culture

Response of plasma membrane to applied hydrostatic pressure in chondrocytes and fibroblasts

Effects of applied hydrostatic pressure on transmembrane potentials were investigated in sheep articular chondrocytes and human skin fibroblasts in non-confluent monolayer cultures. Resting potentials in chondrocytes (about -12 mv) and in fibroblasts (about -15 mV) were increased and decreased respectively by over 40% after pressure was applied cyclically (0.33 Hz, 120 mm Hg, 20 minutes). Continuous pressure (120 mm Hg, 20 minutes) caused deplorization in both cell types. Low frequency pressure application (less than 0.08 Hz) caused depolarization in chondrocytes and hyperpolarization in fibroblasts. Quinidine (2 x 10(-5) M) blocked and verapamil (10(-5) M) reduced hyperpolarization responses, suggesting involvement of Ca(2+)-dependent K+ channels. A23187 (1.9 x 10(-6) M) caused hyperpolarization in chondrocytes, augmented further by subsequent pressure application (0.33 Hz). Tetrodotoxin (10(-6) M) blocked depolarization responses indicating that these were due to Na+ influx. Blockade of histamine H1 receptors by chlorpheniramine maleate (5.1 x 10(-6) M), H2 receptors by cimetidine (7.9 x 10(-6) M) and beta-adrenoreceptors by sotolol (1.3 x 10(-4) M) had no effect on hydrostatic pressure-induced hyperpolarization in chondrocytes. Cytochalasin B (2 x 10(-5) M and at 4 x 10(-6) M) abolished pressure-induced hyperpolarization in chondrocytes; in contrast, applied cyclical hydrostatic pressure to cytochalasin-treated fibroblasts caused hyper-polarization, suggesting that cytoskeletal changes were involved.

Monitoring of the mitochondrial and plasma membrane potentials in human fibroblasts by tetraphenylphosphonium ion distribution

The lipophilic cation tetraphenylphosphonium (TPP+) is accumulated by human skin fibroblasts across both the plasma and mitochondrial membranes. We show here that TPP+ uptake is indeed greatly decreased under conditions leading to de-energization of mitochondria. The TPP+ accumulation in the presence of the proton ionophore FCCP has been used for determination of the plasma membrane potential across the plasma membrane, after correction for potential-independent binding of TPP+ to cellular components. Following this procedure, a value of 75 mV has been obtained. Through the amount of TPP+ released by FCCP treatment, an estimate of the in situ mitochondrial membrane potential has been made. Furthermore, we report that the mitochondrial component of TPP+ accumulation decreases with aging of fibroblast cultures.

Membrane potentials, electrolyte contents, cell pH, and some enzyme activities of fibroblasts

The resting membrane potential of the cultured fibroblasts derived from rabbit subcutaneous tissues was -10.2 +/- 0.20 mV (n = 390). This potential was affected by the potassium concentration in the culture medium, but not by other chemical or hormonal preparations, such as dibutyryladenosine 3',5'-cyclic monophosphate (0.5 to 5.0 mmol/l), sodium fluoride (10(-5) to 10(-4) M), hydrocortisone (10(-7) to 10(-6) M), parathyroid extract (0.5 to 1.0 U/ml), or thyrotrophin (5 to 10 mU/ml). The Na+, K+, and Cl- concentrations of the cultured fibroblasts were 35.4, 85.7, and 22.6 mmol/l cell water, respectively. The water and protein contents of these cells were 82.1 and 9.18 g/100-g cells, respectively. The intracellular pH of fibroblasts as determined by [14C] dimethyloxazolidine-2, 4-dione, and 3H2O ranged between 6.9 and 7.1 when the pH of the culture medium was maintained at 7.4. The activities of Na+, K+-, HCO3(-)-, and Ca++, Mg++-ATPases in these cultured cells were 19.0 +/- 2.1, 13.6 +/- 2.1, and 6.6 +/- 1.2 nmol pi/mg protein per minute, respectively, and the carbonic anhydrase activity was 0.054 U/mg protein. Calculations based on the values for the membrane potential and the electrolyte concentrations observed in this study indicate that Na+, K+, Cl-, and H+ are not distributed according to their electrochemical gradients across the cell membrane. Na+, Cl-, and H+ are actively transported out of the cells and K+ into the cells.

Inhibition of interferon production and antiviral action in mouse cells by 4,5',8-trimethylpsoralen activated with near ultraviolet light. Brief report

The DNA of mammalian cells treated with 4,5',8-trimethylpsoralen (Trioxsalen) is crosslinked (preventing transcription) only after photoactivation with near ultraviolet light. Suppression of gene action in cocultivated or fused cultures, including both induction and antiviral action of fibroblast interferon, can consequently be limited to pretreated cells, an advantage over actinomycin treatment.

Myotonic muscular dystrophy: abnormalities in fibroblast culture

Skin fibroblasts in culture, derived from four unrelated patients with myotonic muscular dystrophy, contain abnormally large amounts of material with the staining characteristics of acid mucopolysaccharide. These cells also differ from normal cells in their pattern of growth at a high density in culture.