Membrane electroporation (MEP) induces a drastic change in membrane conductance and permeability. However, the underlying mechanisms by which MEP-induced currents (I(MEP)) are generated or resealed remain unclear. In this study, we investigated how the fluctuations of I(MEP) might be elicited in different types of cells, including pituitary GH(3) cells, NG108-15 neuronal cells, and RAW 264.7 macrophages. We applied the detrended fluctuation analysis (DFA) to analyze the current signals in response to large hyperpolarizations. The DFA exponents from the current signals at 10 s preceding the start of the initial I(MEP) (I(Pre)) in GH(3) cells exhibited two components (short time lag [α(1)] and long time lag [α(2)]) with a crossover threshold of about 7 ms. The α(1) value was 0.46 ± 0.04 (n = 7), whereas the α(2) value with 0.62 ± 0.05 (n = 7) indicated the presence of long-term correlations of current signals. However, during maximal I(MEP), the slope of double logarithmic plot was linear and estimated to be 0.99 ± 0.02 (n = 8) with no clear crossover. Upon changes in membrane polarization, neither short- nor long-range correlation was altered. Chloroquine (CQ), a lysosomotropic agent, decreased the I(MEP) amplitude with an IC(50) value of 46 μM; however, it had no effects on the scaling exponents of I(Pre) or I(MEP). Although CQ or membrane polarization altered the amplitudes of I(MEP), no changes in correlation properties of this current were detected. The scaling exponents derived from I(Pre) exhibit long-range correlations in these different types of cells, indicating there is a correlated character of the electropore dynamics that may be allowed to predict the MEP process.

DEHP (bis(2-ethylhexyl)-phthalate) known to be an endocrine-disrupting chemical is a widely used phthalate. Little information regarding the effects of phthalate esters on ion currents is available. In this study, the effects of DEHP and other phthalate esters (DBEP: di(2-butoxyethyl)-phthalate and DMGP: di(2-methylglycol)-phthalate) on ion currents were investigated in pituitary GH₃ cells. Hyperpolarization-elicited K⁺ currents in GH3 cells bathed in high-K⁺, Ca²⁺-free solution were examined to evaluate the effects of DEHP, DBEP, and DMGP on the ether-a`-go-go-related-gene (erg) K⁺ current (IK(erg)). Addition of DEHP to GH₃ cells suppressed the amplitude of IK(erg) in a concentration-dependent manner with an IC₅₀ value of 16.3 μM. With a two-pulse protocol, addition of DEHP shifted the activation curve of IK(erg) to a depolarized potential by approximately 10 mV with no change in the rate of IK(erg) deactivation. This compound did not have any effects on delayed rectifier K⁺ current in GH₃ cells, while 4-aminopyridine-3-methanol (100 μM) suppressed this current significantly. DBEP (30 μM) had little or no effect on IK(erg), while DMGP (30 μM) slightly reduced it. In inside-out configuration, DEHP (30 μM) applied to the bath slightly reduced the activity of large-conductance Ca²⁺-activated K⁺ channels. DEHP (30 μM) increased the frequency of spontaneous action potentials (APs); however, this compound at the same concentration had no effect on AP firing in KCNH2 siRNA-transfected GH₃ cells. The effects described herein can contribute to their actions on functional activity of endocrine or neuroendocrine cells if similar results are found in vivo.

There is a direct association of Na(+) and K(Na) channels which can provide the rapid activation of K(Na) channels required to regulate AP firing occurring in motor neurons.

The effects of (2-hydroxypropyl)- β-cyclodextrin (HPβCD), a cyclic oligomer, on membrane electroporation-induced inward current (I_MEP) in pituitary tumor (GH₃) cells were experimentally and analytically characterized. Depletion of membrane cholesterol by exposing cells to HPβCD (2 mM) increased the activation time constant of delayed rectifier K⁺ current. Such maneuver resulted in a significant reduction of I_MEP density. 2,2’-Azo-bis(2-amidinopropane) dihydrochloride (AAPH), an initiator of free radicals, increased the magnitude of I_MEP. AAPH-stimulated I_MEP was not reversed by the blockers of Ca²⁺-activated K⁺ channels, but by LaCl₃ or MnCl₂. However, in HPβCD-treated cells, the ability of AAPH to enhance I_MEP was abolished. Under such maneuver, the gating charge of I_MEP activation was increased by 2 fold, along with a hyperpolarized shift of the activation curve by 30 mV. No change in single-channel conductance of MEP-induced channels during cell exposure to HPβCD was demonstrated. The energy change of I_MEP in untreated and HPβCD-treated cells was estimated to be -17.7 and -44.8 kJ/mol, respectively, and the perturbation of free energy following HPβCD treatment was -27.1 kJ/mol. Based on an MEP model, cell exposure to HPβCD increased the edge energy of the electropore size. By use of a two barrier-one site barrier model, HPβCD treatment can increase both the peak height and well depth of the barrier profile. Taken together, depletion of membrane cholesterol by HPβCD can elevate the edge energy of pore formation, thereby decreasing the I_MEP magnitude. The channel-suppressing properties during membrane cholesterol depletion with HPβCD might thus contribute to the underlying mechanisms by which such maneuver alters neuronal or neuroendocrine function.