1. Acetylcholine (ACh)- a neurotransmitter- ALWAYS causes an excitatory response on the plasma membranes of skeletal muscle cells. It acts to open ion channels that will cause a major influx of Na+ into the muscle cell.This leads to an end-plate potential which depolarizes the membrane and leads to an action potential in the muscle membrane. The action potential spreads through the entire membrane and down the T-tubules (which are continous w/ the membrane). In the T-tubules, there are voltage DHP receptors that respond to the action potential and physically pull open ryanodine channels. Ryanodine channels opening allows for Ca2+ to flow out of the sarcoplasmic reticulum. This calcium binds to troponin, which shifts tropomysin out of the way to expose the actin binding sites. Myosin heads can now bind (w/ ATP) and the muscle contracts.
2. water cells? - I'm not sure what you're asking- water could never become hydrophobic (water fearing, hating). However, if water channels (aquaporins) mutated into hydrophobic channels, water could neither leave nor enter the cell. This would be a huge problem. Take for instance your kidneys, the first part of your urinary system. IF you couldn't move water from the tubules and back into your blood, you would have to drink 180 (I think) liters of water a day. This is almost impossible! If you didn't your blood would get so thick, it would severely slow down your blood flow, meaning you may not be able to deliver adequate amounts of oxygen to all your vital organs in a timely manner. I hope this helps.