| dc.contributor.author | Tao, Qianping. | en_US |
| dc.date.accessioned | 2014-10-21T12:36:30Z | |
| dc.date.available | 1997 | |
| dc.date.issued | 1997 | en_US |
| dc.identifier.other | AAINQ24762 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55502 | |
| dc.description | The retinal pigment epithelium (RPE) is a monolayer of cuboidal cells which lies in close association with the photoreceptors of the neural retina. This epithelium is an indispensable component of the retina and has diverse functions which are essential for the maintenance of retinal viability. The RPE participates in both regulation of the ionic concentration within the subretinal space as well as the maintenance of the homeostasis of the microenvironment surrounding the photoreceptors. | en_US |
| dc.description | In this study, membrane potential and ionic conductances as well as their modulation by adrenergic agonists were studied in cultured rabbit RPE cells using whole-cell, perforated-patch, and single-channel patch-clamp recording techniques. RPE cells had a mean membrane capacitance of 27.0 $\pm$ 0.8 pF (SE, n = 294). The resting membrane potential averaged $-$31.0 $\pm$ 1.4 mV (SE, n = 110), but was as high as $-$60 mV in some cells. When K$\sp+$ was the principal cation in the recording electrode, depolarizing voltage steps from a holding potential of $-$60 mV activated outwardly rectifying currents. These depolarization-activated outward currents were apparent in 80% of cells studied. Tail current analysis revealed that the outward currents were primarily K$\sp+$ selective. The outwardly rectifying K$\sp+$ current (I$\rm\sb{K}$) was the most frequently observed conductance in RPE cells and resembled the delayed rectifying K$\sp+$ current described in other cells. I$\rm\sb{K}$ was blocked by tetraethylammonium ions (TEA$\sp+)$ and barium (Ba$\sp{2+})$ and reduced by 4-aminopyridine (4-AP). In a small number of cells (7%), depolarization to $-$50 mV or more positive potentials evoked a fast-inactivation outward K$\sp+$ current (I$\rm\sb{Ki}$). An inwardly rectifying K$\sp+$ current (I$\rm\sb{Ki}$) was also present in 40% of cells. I$\rm\sb{Ki}$ was blocked by extracellular Ba$\sp{2+}$ or cesium (Cs$\sp+$) and exhibited time-dependent decay at negative potentials, due to Na$\sp+$ blockage. | en_US |
| dc.description | The manipulation of cytosolic free Ca$\sp{2+}$ ((Ca$\sp{2+}$) $\rm\sb{i}$) revealed a Ca$\sp{2+}$-activated component of I$\rm\sb{K}$. Studies of Ca$\sp{2+}$-activated K$\sp+$ current $\rm I\sb{K(Ca)})$ were carried out by increasing the extracellular Ca$\sp{2+}$ concentration $\rm (\lbrack Ca\sp{2+}\rbrack\sb0)$ in the presence of a Ca$\sp{2+}$ ionophore, ionomycin. $\rm I\sb{K(Ca)}$ was blocked by iberiotoxin (IbTX), a specific maxi-K$\rm \sb{Ca}$ channel blocker. Single channel recording from cell-attached and excised membrane patches confirmed the presence of large conductance Ca$\sp{2+}$-activated K$\sp+$ channels which could be classified as maxi-K$\rm \sb{Ca}$ channels based on: (1) the large unitary conductance ($>$220 pS with 130 mM K$\sp+$), (2) the voltage dependence, (3) the dependence of the current reversal potential on the transmembrane K$\sp+$ gradient, and (4) the (Ca$\sp{2+}$) $\sb{\rm i}$ dependence. Further experiments demonstrated that maxi-K$\rm \sb{Ca}$ channels in rabbit RPE cells are modulated by the activation of $\alpha\sb1$-adrenoceptor coupled signalling pathway(s). Calcium released from intracellular stores by IP$\sb3$ following $\alpha\sb1$-adrenoceptor activation, enhanced maxi-K$\rm\sb{Ca}$ channel activity. | en_US |
| dc.description | The K$\sp+$ conductances reported here may provide conductive pathways which are important for maintaining ion and fluid homeostasis within the subretinal space, and may be also involved in other important cellular functions vital to the photoreceptors. This study also provides evidence for a role for $\alpha\sb1$-adrenoceptors in the modulation of maxi-K$\rm\sb{Ca}$ channels in rabbit RPE cells. The modulation of maxi-K$\rm\sb{Ca}$ channels may contribute to the physiological regulation of K$\sp+$ transport and other important functions in this cell type. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1997. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Biology, Cell. | en_US |
| dc.subject | Health Sciences, Pharmacology. | en_US |
| dc.subject | Biology, Animal Physiology. | en_US |
| dc.title | Characterization and modulation of ionic conductances in cultured rabbit retinal pigment epithelial (RPE) cells. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
